Synthesis of 3,4- dihydroquinazolinones via ring closure or reduction

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SYNTHESIS OF 3,4-

DIHYDROQUINAZOLINONES VIA RING CLOSURE OR REDUCTION

Bachelor thesis in Chemistry

by Adam Hallberg

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Abstract

Three kinds of 3,4-dihydroquinazolinone analogues were successfully synthesized and isolated from methyl 2-formylphenyl carbamate through a one-pot two step synthesis using microwave irradiation and formic acid. The overall aim of synthesizing reduction products was tested using different amines, observing that highly nucleophilic amines were prone to form ring closed products. Among the six amines used in synthesis only three products were isolated and characterized using a combination of mass spectrometry and nuclear magnetic resonance, NMR. Two of the products, 3a and 3d, had previously not been described.

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ABBREVIATIONS

In order of appearance.

3,4-DHQ 3,4- dihydroquinazolinone DOS Diversity oriented synthesis

AIDS Acquired immune deficiency syndrome HIV-1 Human immunodeficiency virus 1

2-ABA 2-aminobenzylamine

MW Microwave

2-ABAlc 2-aminobenzyl alcohol

AcOH Acetic acid

HCOOH Formic acid

MeOH Methanol

DCM Dichloromethane

EtOH Ethanol

EtOAc Ethyl acetate

LC/MS Liquid chromatography and mass spectrometry

MS Mass spectrometry

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INTRODUCTION Overview

In the world of modern medicine, the design-make-test-analyze cycle to find new biologically active chemical leads is central to drug discovery and chemical biology¹. There exist some compounds that can be thought of as backbone structures or core structures for the development of new drugs. The increased threat of drug-resistant bacteria also makes it crucial to synthesize new medicinal compounds to be used clinically². Quinazolinones are nitrogen containing heterocycles found in various naturally occurring alkaloids³. Their benzannulated analogues, dihydroquinazolinones are of pharmacological interest for various reasons because of their biological activity, which will be referred back to in later sections⁴. Synthesis of these molecules can be done using palladium-catalyst from electron-rich arylamines in 4-nitrophenol

5. Selective acylation of aliphatic amino groups using Zr(azobenzene-4,4’-dicarboxylate) is yet another method by which DHQ are produced⁴. The development of these backbones usually requires strong acids or transition metals to help the synthesis as development for a simple, effective and reliable reactions has not been realized yet⁶. There has been much research in the field of 2,3-substituded dihydroquinazolinones but less concerning the 3,4-substituted ones.

Some substituted dihydroquinazolinones are depicted in figure 1. These exhibit the 3,4- dihydroqinazolinone (3,4-DHQ) backbone and are examples of how the structure is developed in modern medicine. 3,4-DHQ is the most common derivative of DHQ however, information is scarce⁷. It could be that the 3,4-substituted form exists in equilibrium with its tautomeric 1,4- dihydro form, but the 1,4 form has only been isolated in cases where the 1 and 2 positions of the heterocycle are substituted with an alkyl or aryl group⁷. To achieve the need for new and diverse small organic molecules, a synthesis strategy known as diversity-oriented synthesis (DOS) has emerged. The strategy includes different methods, one of which is the branching cascade method used to create complex libraries with a plethora of polyfunctionalized molecules and limited waste generation⁶. While other methods are included in DOS, the reason branching cascade reactions has gained such large attention is partly because of its one-step or pot process utilizing one or many polyfunctionalized precursors with different reagents and varying conditions to generate a multitude of diverse molecules¹. The versatility 3,4-DHQ makes it interesting and compelling thus; efforts to synthesize the compound cheaply and effectively is in the interest for many pharmacological companies.

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Figure 1: Examples of how the DHQ backbone can be developed into modern medicine^8,9.

The properties of DHQ

The quinazolinones display biological activity and are thus an important class of molecules¹⁰ worth researching. Specifically the 3,4-DHQ scaffold is important in medicinal chemistry due to its possibility to suppress growth in human cancer cells when further developed⁵. The C4-substituted quinazolinone framework can for example act as a Na⁺/Ca²⁺

channel blockers, something exemplified by SM-15811^8,11 depicted in figure 2. Furthermore, DHQs have been studied as an inhibitor of trypanothione reductase, an enzyme of the parasite Trypanosoma brucei⁴. 3,4-DHQ have also made ample advancement as a potent non- nucleoside in the fight against acquired immune deficiency syndrome (AIDS) and human immunodeficiency virus type-1 (HIV-1)¹².

Figure 2: The sodium-potassium channel blocker SM-15811¹¹

Derivatives of quinazolinones are very useful as vasodilatory, antifungal, antimicrobial, analgesic, sedative, anticonvulsant and a lot more; some have even been on the market as a treatment for cancer². Derivatives containing the 3,4-DHQ scaffold has been found to a potent inhibitor of enzymes like trypanothione reductase and acetylcholinesterase as well as an antitumor, anticancer agent¹³. Because of their use in many modern drugs the 3,4-DHQ scaffold is an interesting substance and various synthetic routs have been developed to access this framework.

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Classic methods for synthesis

There are many ways to synthesize compounds with the quinazolinone backbone, some make use of metals such as palladium and copper often involving many steps. Some use less environmentally friendly methods, such as using reagents that could be dangerous like strong acids and transition metals⁶. 3,4-Dihydroquinazolines can be obtained by the selective reduction of the quinazoline ring, using heterocyclization of o-aminobenzylamines or o- nitrobenzylamines (scheme 1), and through the reaction of o-acylanilines with formamide or urea in formic acid⁷. The most common methods for synthesizing according to Stevens et al.

(2015) is cyclization/reduction sequence starting from 2-trichloroacetamidobenzophenones, or the reaction between o-acyl or o-amino anilines with a carbonyl compound or by using Grignard reagent¹⁴.

Scheme 1: A well-established literature procedure (Yamamoto procedure) for synthesizing dihydroquinazolines¹⁰

Other methods have involved cyclic precursors like quinazolinones, quinazolines or tetrahydroquinazolines which are either reduced or oxidized to give dihydroquinazolines.

Another common synthesis pathway employs 2-aminobenzylamine (2-ABA) as precursor which is set to react with amidines, carboxylic acid or aldehydes in oxidative conditions to yield N-unsubstituted dihydroquinazolines⁴. Another approach using 2-ABA is to make a heterocycle of functionalized 2-ABA which often require drastic reaction conditions or prolonged reaction time⁴.

Supplementary methods include nucleophilic addition reactions to secondary amines followed by intramolecular conjugate addition or copper catalyzed annulation of N- arylamidines⁴. The aza-Prins cyclisation of N-substituted homoallylic amine component have been used to synthesize numerous biologically active alkaloids⁶. The Mannich reaction has been used for the asymmetric synthesis of 3,4-DHQ it is limited by the need for strong electrophiles like trifluoromethyl ketimines. Some other methods that have been reported use Pd-catalyzed domino Heck amidation-Michael addition from o-haloanilines and another had developed a chiral diamine-Brønsted acid-catalyzed asymmetric Mannic reaction¹⁵.

These methods rely on chemicals that are both toxic and rare and that is why new methods using microwave (MW) assisted branching cascade reactions that are better for both people and the environment, has been developed.

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Modern microwave assisted organic synthesis method

Modern methods for synthesizing 3,4-DHQ include using MWs to heat reaction mixtures. This is favorable as most organic reactions require heat and conventional heat transfer methods rely on equipment such as oil baths or heating mantles which, can cause a temperature gradient within the sample¹⁶. These techniques are, however, still widely employed in both research and educational labs. Furthermore, the reaction mixture could locally become overheated leading to product and reactants being degraded or decomposed. To avoid these potential problems, the reaction will be carried out using MW radiation as the heat transfer method. The MW multicomponent synthesis has become a corner stone in the shift for organic chemistry to more environmentally friendly methods⁹. It has the advantage that it does not require a contact surface for the transfer. Instead the MWs supply energy to the reaction mixture remotely and passes through the reaction flask and invigorates the solution directly by transforming the electromagnetic radiation into heat. Of course, there are some problems with MW assisted organic synthesis, most notably explosion risks due to overheating. These problems can however be overcome by carefully monitoring the heat via thermometers or IR, something that is quite standard in modern synthesis MW ovens. This method of MWs assisted organic synthesis is a revolutionary way speed up reactions that would take a long time, it is especially useful to the field of medicinal chemistry and drug synthesis¹⁶.

Leuckart reaction

The Leuckart reaction is carried out by heating a mixture of the carbonyl compound and the amide or its derivative¹⁷. The reaction is named after scientist Rudolf Leuckart who, in 1885 was first to describe the conversion of certain aldehydes and ketones to their amines¹⁸. The Leuckart reaction can be thought of as the process by which aldehydes and ketones undergo reductive amination using formamide or ammonium formate¹⁷. However, it would be Wallach and Ingersol who popularized the reaction; Wallach by showing that the reaction yielded good results and Ingersol through development of the process. In the reaction ammonium formate dissociates into ammonia and formic acid. The ammonia attacks the carbonyl to form the imine then a subsequent reduction of the imine is made by the formic acid that strips the hydroxyl or if the formic acid is in excess it reduces the imine to an amine through a formyl intermediate. A few sources point to an increased yield when using formic acid^17,18 and that the reaction gives good yields when run around 150°C¹⁷. When studying the mechanism of the Leuckart reaction, Otto Wallach proposed that using formic acid to reduce the imine to the amine whereby the amine then reacts with more formic acid to yield the final product, a substituted formamide¹⁷. The best yields for producing substituted formamide was to use a mixture of formamide and formic acid¹⁸. Wallach found that by using acetic acid or formic acid to a mixture of benzaldehyde and ammonium formate the only product was tribenzylamine¹⁹. To summarize, the Leuckart reaction converts aldehydes and ketones to amines through reductive amination using heat and variegated forms of formates and formamides. Wallach saw the potential and generalized it using formic acid as a catalyst. This

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is the foundation for the reaction carried out in this paper; it builds on, perhaps more Wallach’s research than Leuckart's, the reductive amination of aldehydes and ketones using formic acid as a source of hydride which is the essence of the Leuckart-Wallach reaction.

Aim

The aim of this project is to study the reaction of methyl (2-formylphenyl) carbamate (1) with small set of substituted amines with varying nucleophilic appendages (scheme 2 2a-f) in one-pot two step synthesis where we in the first step use acetic acid (AcOH) and then attempt to reduce the subsequent imine with formic acid (HCOOH). The competing reaction is a nucleophilic aromatic substitution reaction formed by the rings of 2a-2c with the intermediate imine. The idea of using HCOOH to reduce the intermediate imine has its basis in the Leuckart reaction. In the present study a modern MW assisted variation of the Leuckart reaction is utilized to carry out the synthesis where the HCOOH act as a source of hydride. The overarching scheme including initial reaction conditions are shown in scheme 2 together with intended products 3a-f. Herein is presented a metal-free MW-assisted strategy to access libraries of 3,4-DHQ embedded frameworks from commercially available amines with variegated nucleophilic substituents 2a-f.

Scheme 2: R-groups of reagents 2a-f and R-groups of corresponding target products 3a-f.

RESULTS AND DISCUSSION

All experiments carried out were optimized by varying temperature, time and solvent composition to yield the reduced product (see appendix for optimization tables). In cases where no yield is reported steps have been taken to push the reaction toward increased yield of 3a-f.

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Methyl (2-formylphenyl) carbamate (1)

Starting from 2-aminobenzyl alcohol aldehyde 1 was obtained in good yield over 2 steps. Using dilute 2% hydrochloric acid to remove unreacted amine from step 1 proved a significant improvement from the protocol²⁰ provided by Ikeda et al. Following scheme 3 with the additional cleaning step provided the product without need for further purification. The use of manganese dioxide (MnO2) was because of its selectivity toward benzylic alcohols.

Scheme 3: Formation of 1 from starting reagent 2-aminobenzyl alcohol

In the first step the mixture was stirred for 3 and ½ hours while Ikeda et al. reported only 1 hour and even greater discrepancy was observed in the second step where Ikeda et al.

reported 2 hours and here over-night (~16h) reaction was required to reach full conversion.

This may be traced back to the activity of the MnO2 batch used and it may have been less reactive than the one used by Ikeda et al.

3-(2-Phenylethyl)-3,4-dihydro-2(1H)-quinazolinone

Reacting aldehyde 1 and amine 2a in AcOH at 100°C for 10 min under MW radiation and subsequently adding HCOOH and continue the reaction at 130°C for 20 min provided crude product 3a (scheme 4). Based on observations of the liquid chromatography and mass spectrometry (LC/MS) data the reaction appeared to be highly efficient as only the major target product was observed. Purification 3a was done by column chromatography using methanol (MeOH) and methylene chloride (DCM) 1:100 providing pure product 3a.

Scheme 4: Reacting aldehyde 1 with amine 2a to yield product 3a.

3-(2-3,4-Dimethoxyphenylethyl)-3,4-dihydro-2(1H)-quinazolinone

Reacting aldehyde 1 and amine 2b in AcOH afforded solely the ring closed product via electrophilic aromatic substitution, regardless of temperature. Reacting 1 and 2b using dilute AcOH in ethanol (EtOH) provided the necessary acidity for the first step, then probing various temperatures revealed that 110°C gave good results for the first step of the reaction, whereby all starting material had been converted to intermediate imine. Further investigations in the second step revealed that higher temperatures were beneficial to the formation of 3b. However, even at temperatures of 190°C there was still formation of 3b’ (scheme 5), higher temperatures

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were not explored due to pressure constraints on the MW synthesizer. Throughout the process, there was ample competitions between the two competing reactions. Other temperatures tested were 120°C, 150°C, 165°C and 170°C see appendix. Separation of the two compounds was unsuccessful despite various attempts using different mixtures of DCM, iso-hexane, ethyl acetate (EtOAc) and toluene.

Scheme 5: Reacting 1 and 2b gave two inseparable products 3b and 3b’

3-(2-Tryptamine)-3,4-dihydro-2(1H)-quinazolinone

Reacting aldehyde 1 with amine 2c with diluted AcOH in ethanol yielded a mixture of 3c and 3c’ at room temperature, as revealed by LC/MS spectrometry. However, increasing the temperature only yielded more of 3c’ while 3c, the desired product from scheme 2, was not observed. Scheme 6 shows what was attempted and the products that were determined using LC/MS. The reason that we observe both product even in dilute conditions is most likely because of 2c’s nucleophilicity and the trend observed by Lakhdar et al. (2006)²¹. It is likely that we get electrophilic aromatic substitution reaction. The same argument can be made for the observation of 3b’. When attempting with just acetic acid only 3c’ was observed and increasing the temperature pushed the reaction toward more of 3c’ (see appendix). Based on these results and a lack of selectivity toward formation of 3c decision was made to discontinue studies on this substrate.

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Scheme 6: Reaction between 1 and 2c to yield both 3c and 3c’

3-(2-Hydroxyethyl)-3,4-dihydro-2(1H)-quinazolinone

Reacting aldehyde 1 and amine 2d yielded an ester intermediate after the second step.

The ester was hydrolyzed in a third step using a saturated solution of potassium carbonate K2CO3 in water. The crude product was purified using column chromatography and yielded 3d in 53%. Scheme 7 provides depicts this three-step process. The formation of an ester is because the primary alcohol is susceptible to a Fischer esterification under the acidic reaction conditions.

Scheme 7: Conversion of aldehyde 1 and amine 2d to yield 3d in a 3 step synthesis 3-(2-Methoxyethyl)-3,4-dihydro-2(1H)-quinazolinone

Reacting 1 and 2e yielded 3e in 54% yield over 2 steps (scheme 8) and with subsequent purification using column chromatography with Iso-hexane in EtOAc (1:9). Compared to the process of acquiring 3d it is very similar with the biggest difference being the esterification which did not happen in the case with 3e. Another difference is that the time in the first step is two times longer and the temperature and time of the second step is both higher and longer.

The yields are roughly equal despite the process for 3e is less involved. Upon analyzing the

13C-NMR for 3e an unexplained peak was discovered around 30ppm, at first it was thought to originate from some solvent, possibly acetone, but there was not anything to support that idea in the ¹H-NMR of the compound. Thus the peak remains an enigma.

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Scheme 8: Reaction between 1 and 2e to yield 3e 3-(2-ethyl-3-aminopropanoate)-3,4-dihydro-2(1H)-quinazolinone

Reacting 1 with 2f in AcOH then evaporating the AcOH before adding 2 mL of HCOOH in EtOH (1:9) showed some good results based on the LC/MS readings. Reacting it according to the general scheme (scheme 1) resulted in hydrolysis of the ester to carboxylic acid. Using only 1 mL of HCOOH in EtOH without evaporating the AcOH gave the same result as the general scheme. Due to time constraints, further optimization of the reaction and subsequent isolation was unable to be performed. Future studies should focus on the further development of this reaction and isolation of the desired product.

Scheme 9: Reaction scheme for formation of 3f from aldehyde 1 and amine 2f

When attempting to synthesize 3b and 3c we observe competition from the nucleophilic aromatic substitution reaction in the second step from the appendage of amines 2b and 2c. In the first step of the reaction it’s important that the amine is nucleophilic enough to cause the ring to close and the imine to form. While in the second step we observed that depending on the nucleophilicity of the substituent, we either get the ring closed products or reduction product.

CONCLUSION

In conclusion, the MW-assisted cyclization of methyl (2-formylphenyl) carbamate with six different amines has been examined. Reactions with amines equipped with highly nucleophilic substituents were unsuccessful in producing the desired targets however, there was a distinct correspondence between the nucleophilicity of the appendages and their propensity for cyclization as captured by figure 5. Arrays of multiple trials notwithstanding no modification to this particular method was identified to quell the formation of undesired byproduct. Amines 2a, 2d and 2e yielded C4-unsubstitudted 3,4-DHQ in isolated yields of 53-66%. No product was isolated from amine 2f due to insufficient time however, progress into identifying necessary reaction conditions was made. Based on the results, the author suggests a course of action to further exploration into less electron-rich substituents and amines incapable of undergoing cyclization.

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Figure 5: 2a-c from left to right increasing nucleophilicity²¹

ACKNOWLEDGEMENTS

I wish to thank the institution of pharmaceutical chemistry for affording me this opportunity to do my thesis work. Special thanks to Professor, PhD Luke Odell who was my supervisor and has guided me. I want to thank him for his tenacity and unwavering want to help me. Thanks also to PhD. Luke Schembri who apprised and guided me in the lab. I would also like to direct thanks to the rest of the department and everyone who have helped and supported me and made this project fun and fulfilling.

METHOD AND MATERIALS

Materials

APPARATUS

An NMR machine, the SampleXpress from Bruker running at 400 MHz was used to determine and analyze structures. An LC machine coupled with mass spectrometry was used to monitor reaction progression. The MW machine used was a Biotage initiator EXP US 400W MW synthesizer schematic shown in Figure 4. The LC machine was an Ultimate 3000 HPLC from Thermofisher scientific with an attached MSQ Plus Mass detector with detection similar to a single-quadrapole. The LC pump, LC column compartment, autosampler and variable wavelength array were all delivered from Dionex part of the ultimate 3000 series.

SOFTWARE

The NMR were analyzed using Mestrenova. Molecules and reaction schemes and general figures were all drawn in Chemdraw professional 15.1. The mass spectrometry and uv/vis was analyzed using Chromelon by Dionex Corporation, version 6.80.

EXPERIMENTAL SECTION

General

All reagents and solvents were obtained from commercial suppliers and used without further puriﬁcation. The yields stated refer to homogenous and spectroscopically pure isolated

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material. Thin layer chromatography (TLC, 0.25 mm E. Merck silica plates, 60F-254) was used to assess reaction progress and the plates were visualized with 254 nm UV light. Silica gel chromatography was performed using E. Merck silica gel (60 Å pore size, particle size 40−63 nm). ¹H NMR spectra were recorded at 400 MHz and ¹³C NMR spectra at 100 MHz the chemical shifts for ¹H NMR and ¹³C NMR were referenced to tetramethylsilane via residual solvent signals (¹H, CDCl3 at 7.26 ppm;¹³C, CDCl3 at 77.16 ppm). MW reactions were performed in an Initiator single mode reactor producing controlled irradiation at 2450 MHz and the temperature was monitored using the built-in online IR sensor. LC/MS was performed on an instrument equipped with a CP-Sil 8 CB capillary column (50 × 3.0 mm², particle size 2.6 μm, pore size 100 Å) operating at an ionization potential of 70 eV using a CH3CN/H2O gradient (0.05% HCOOH). Mass values were determined using a 7-T hybrid ion trap and a time of ﬂight detector and an electrospray ionization source. All reactions were performed in sealed Pyrex MW- transparent process vials designed for 0.5−2 mL reaction volumes, unless otherwise stated. All evaporations were carried out using a rotation evaporator. ⁴When analyzing the ¹³C-NMR for 3e an unexplained anomaly was discovered around 30ppm, the peak was first thought to originate from some solvent but there was nothing to support that in the ¹H-NMR of the compound.

Procedure to synthesize methyl (2-formylphenyl) carbamate (1)

A round bottom flask was charged with 2-ABA (1.0 g, 8.2 mmol) 40mL of THF:H2O (2:1 ratio), methyl chloroformate (1.0 mL, 12.9 mmol) and potassium carbonate (11.2 g, 81.0 mmol). The reaction was monitored every 30 min with TLC using DCM as mobile phase and after 2 and a half hour it was complete. To the round bottom flask approximately 20 mL of water was added and the resultant mix was extracted with ethyl acetate. The extracts were washed three times with dilute 2% HCl (aq) (10 mL). The extracts were dried using magnesium sulfate and filtered. A small amount of pale-yellow liquid was left after evaporation and to this was added 40 mL of DCM and manganese dioxide (6.1 g, 69.8 mmol). This was then stirred and monitored with TLC using EtOAc and iso-hexane (1:2). The reaction was left over-night (roughly 16 hours). When completed it was filtered through celite. The filtrate was clear and the DCM was evaporated. The precipitate was a light-yellow solid. Total amount was about 1 g (0.9664g, 5.39mmol), corresponding to a yield of 66%. ¹H NMR (400 MHz, Chloroform-d) δ 10.62 (s, 1H), 9.91 (s, 1H), 8.46 (d, J = 8.5 Hz, 1H), 7.64 (ddd, J = 7.0, 6.4, 1.6 Hz, 1H), 7.59 (dd, J = 8.5, 1.3 Hz, 1H), 7.17 (ddd, J = 7.5, 7.5, 1.0 Hz, 1H), 3.81 (s, 3H).

Procedure to synthesize 3-(2-Phenylethyl)-3,4-dihydro-2(1H)-quinazolinone (3a)

A Pyrex vial 0.5-2mL was charged with aldehyde 1 (50 mg, 0.28 mmol), nucleophilic amine 2a (51mg, 0.42 mmol) and AcOH (1 mL). The vial was sealed and subjected to MW irradiation at 100 °C for 10 min and analyzed with LC/MS, after which HCOOH (1 mL) was added. The vial was heated by MW at 150 °C for 20 min, and was subsequently concentrated. Silica gel chromatography (1% MeOH in DCM) provided the title compound as a white solid (45.0 mg,

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66.1%). ¹H NMR (400 MHz, Chloroform-d) δ 7.37 (s, 1H), 7.32 – 7.19 (m, 5H), 7.15 (ddd, J

= 7.9, 7.9, 1.8 Hz, 1H), 6.95 (d, J = 5.9 Hz, 1H), 6.91 (ddd, J = 7.3, 7.3, 1.0 Hz, 1H), 6.68 (dd, J = 7.9, 1.1 Hz, 1H), 4.34 (s, 2H), 3.72 – 3.60 (m, 2H), 3.01 – 2.92 (m, 2H).¹³C NMR:(101 MHz, Chloroform-d) δ 154.4, 139.2, 137.1, 129.0, 128.7, 128.3, 126.5, 125.6, 122.0, 117.7, 113.6, 49.5, 49.4, 33.9. Mass spectrometry (MS) (ESI): calcd for C16H17N2O [M + H]⁺: 253.3 found m/z 253.2.

Procedure to synthesize 3-(2-3,4-Dimethoxyphenylethyl)-3,4-dihydro-2(1H)-quinazolinone (3b) A Pyrex vial 0.5-2mL was charged with aldehyde 1 (50 mg, 0.28 mmol), nucleophilic amine 2b (75 mg, 0.42 mmol) and AcOH/EtOH (1:9, 1 mL). The vial was sealed and subjected to MW irradiation at 100 °C for 60 min and analyzed with LC/MS, after which HCOOH (1 mL) was added. The vial was heated by MW at 190 °C for 20 min, and was subsequently concentrated per previous protocol. MS (ESI): calcd for C18H21N2O3 [M + H]⁺: 313.3 found m/z 313.2. MS (ESI): calcd for C18H19N2O3 [M + H]⁺: 311.3 found 311.2¹.

Procedure to synthesize 3-(2-Tryptamine)-3,4-dihydro-2(1H)-quinazolinone (3c)

A Pyrex vial 0.5-2mL was charged with aldehyde 1 (54 mg, 0.30 mmol), nucleophilic amine 2c (67 mg, 0.42 mmol) and AcOH/EtOH (1:9, 1 mL). The vial was sealed and a sample (0.1 mL) was analyzed with LC/MS. MS (ESI): calcd for C18H18N3O [M + H]⁺: 291.3 found m/z 293.2. MS (ESI): calcd for C18H15N3O: 289.3 found m/z 290.2².

Procedure to synthesize 3-(2-Hydroxyethyl)-3,4-dihydro-2(1H)-quinazolinone (3d)

A Pyrex vial 0.5-2mL was charged with aldehyde 1 (51 mg, 0.28 mmol), nucleophilic amine 2d (27 mg 0.42 mmol) and AcOH (1 mL). The vial was sealed and subjected to MW irradiation at 100°C for 30 min and analyzed with LC/MS, then charged with HCOOH (1mL). The vial was heated by MW radiation at 100°C for 40 min. A saturated solution of potassium carbonate in water (5 mL) was added and the reaction was left stirring at 60°C for 60 min. The crude product was then extracted using DCM and purified with column chromatography using EtOAc: MeOH (19:1) and concentrated. The precipitate a white solid. (29 mg, 53%). ¹H NMR (400 MHz, Chloroform-d) δ 8.36 (s, 1H), 7.13 (ddd, J = 7.4, 7.4, 1.0 Hz, 1H), 7.03 – 6.87 (m, 2H), 6.73 (d, J = 7.9 Hz, 1H), 4.54 (s, 2H), 3.86 (t, J = 5.1 Hz, 2H), 3.60 (t, J = 5.0 Hz, 2H).

13C NMR (101 MHz, Chloroform-d) δ 156.2, 136.7, 128.4, 125.5, 122.2, 117.5, 114.0, 61.3, 50.8, 50.3. MS (ESI): calcd for C10H13N2O2 [M + H]⁺: 193.2 found m/z 193.4

Procedure to synthesize 3-(2-Methoxyethyl)-3,4-dihydro-2(1H)-quinazolinone (3e²¹)

A Pyrex vial 0.5-2mL was charged with aldehyde 1 (50 mg, 0.28 mmol) and nucleophile 2e (38 mg, 0.42 mmol) and AcOH (1 mL). The vial was capped and subjected to MW irradiation for 1 hour at 100°C and subsequently analyzed with LC/MS, then charged with HCOOH

1 The second mass refers to product 3B’

2 The second mass refers to product 3C’

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(1mL). The vial was heated by MW radiation at 130°C for 55 min and it was concentrated in vacuo. It was purified with column chromatography Hexane: AcOEt (1:9) to give a white solid.

(30mg, 53%). ¹H NMR (400 MHz, Chloroform-d) δ 7.38 (s, 1H), 7.14 (ddd, J = 7.9, 7.3, 1.0 1H), 7.02 (d, J = 7.3 Hz, 1H), 6.92 (ddd, J = 7.5, 7.5, 0.9 Hz, 1H), 6.68 (d, J = 7.9 Hz, 1H), 4.59 (s, 2H), 3.67-3.66 (m, 4H), 3.37 (s, 3H). ¹³C NMR (101 MHz, Chloroform-d) δ 137.0, 128.2, 125.6, 122.1, 118.1, 113.7, 71.7, 59.1, 50.5, 47.5MS (ESI): calcd for C11H15N2O2 [M + H]⁺: 207.2 found m/z 207.3

Procedure to synthesize 3-(2-ethyl-3-aminopropanoate)-3,4-dihydro-2(1H)-quinazolinone (3f) A Pyrex vial 0.5-2mL was charged with aldehyde 1 (50 mg, 0.28 mmol) and nucleophile 2f (66 mg, 0.56 mmol) and AcOH (1 mL). The vial was capped and subjected to MW irradiation for 30 min at 150°C and subsequently analyzed with LC/MS, then charged with HCOOH/

EtOH (1:9, 2mL). The vial was heated by MW radiation at 100°C for 75 min. MS (ESI): calcd for C13H17N2O3 [M + H]⁺: 249.2 found m/z 249.2

APPENDIX WITH DATA

If nothing else is stated, assume 1:9 ratio of acid: solvent for those cases where solvent is used.

NMR for aldehyde 1

Figure A1: ¹H NMR spectra for 1

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Optimization of reaction parameters for formation of 3a Table A1: optimization of step one for 3a

Entry Acid (mL) Solvent Temp (°C) Time (min)

1 AcOH (1) - 100 10

2 AcOH (1) - 100 10

Table A2: optimization of step two for 3a

Entry Acid (mL) Solvent Temp (°C) Time (min) Yield (%)

1 HCOOH (1) - 100 20 -

2 HCOOH (1) - 150 20 64

LC/MS data 1

Figure A2: Chromatogram for step one for 3a Table A3: m/z response and retention time for step one for 3a

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Figure A3: Mass peaks for 3a 2

Figure A4: Chromatogram of step one for 3a Table A4: m/z responses and retention time for step one for 3a

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Figure A5: Chromatogram of step two for 3a Table A5: m/z responses and retention time for step two for 3a

Figure A6: Chromatogram of purified 3a Table A6: m/z response and retention time for purified 3a

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Figure A7: Mass peaks for purified 3a NMR of 3a

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Figure A8: ¹H NMR spectra for 3a

Figure A9: ¹³C NMR spectra for 3a Optimization of reaction parameters for formation of 3b Table A7: optimization table for step one for 3b

1 AcOH (1) - 100 10

2 AcOH (1) EtOH 100 60

3 AcOH (1) EtOH 100 60

4 AcOH (1) EtOH 120 60

5 AcOH (1) EtOH 110 60

6 AcOH (1) EtOH 110 60

7 AcOH (1) EtOH 110 60

8 AcOH (1) EtOH 110 60

Table A8: optimization table for step two for 3b

1 HCOOH (1) - 120 20 -

2 HCOOH (1) - 150 20 -

3 HCOOH (1) - 130 20 -

4 HCOOH (1) - 120 20 -

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5 HCOOH (1) - 165 20 -

6 HCOOH (2) - 170 20 -

7 HCOOH (1) - 180 20 -

8 HCOOH (1) - 190 20 -

LC/MS data showing progression 1

Figure A10: Chromatogram of step two for 3b and 3b’

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Table A9: m/z responses and retention time

Figure A11: Mass peaks for 3b

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2

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Figure A13: Mass peaks for 3b 3

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Figure A15: Mass peaks for 3b’

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Figure A16: Mass peaks for 3b 4

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5

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6

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7

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8

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Optimization of reaction parameters for formation of 3c Table A17: Optimization table for step one for 3c

1 AcOH (1) - 100 10 -

2 AcOH (1) - 100 20 -

3 AcOH (1) EtOH 110 30 -

4 AcOH/HCOOH

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EtOH 100 30 -

LC/MS data 1

Figure A31: Chromatogram of step one for 3c and 3c’

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Figure A32: Mass peaks for 3c 2

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Figure A34: Mass peaks for 3c’

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3

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4

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Optimization of reaction parameters for formation of 3d Table A22: Optimization table for step one for 3d

1 AcOH (1) - 100 20

2 AcOH(1) - 100 30

3 AcOH (1) - 100 30

Table A23: Optimization table for step two for 3d

1 HCOOH (1) - 100 20

2 HCOOH (1) - 100 40

3 HCOOH (1) - 100 40

Table A24: Optimization table for step three for 3d

Entry Base Solvent Temp (C) Time (h) Yield (%)

1 - - - - -

2 K2CO3 MeOH 40 72 -

3 K2CO3 H2O 60 1.25 53

LC/MS data 1

Figure A39: Chromatogram of step two for 3d

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Figure A40: Mass peaks for 3d

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2

Figure A41: Chromatogram of step two for 3d Table A26: m/z responses and retention time

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Figure A42: Mass peaks of 3d intermediate 3

Figure A43: Chromatogram of step three for 3d

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Figure A44: Mass peaks of 3d

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NMR data for 3d

Figure A45: ¹H NMR spectra of 3d

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Figure A46: ¹³C NMR spectra of 3d Optimization of reaction parameters for formation of 3e Table A28: Optimization table for step one for 3e

1 AcOH - 100 10

2 AcOH - 100 60

Table A29: Optimization table for step two for 3e

1 HCOOH - 100 60 -

2 HCOOH - 130 40 54%

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LC/MS data 1

Figure A47: Chromatogram of step two for 3e Table A30: m/z responses and retention time

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Figure A48: Mass peaks of 3e 2

Figure A49: Chromatogram of step two for 3e

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Figure A50: Mass peaks of 3e

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NMR data for 3e

Figure A51: ¹H NMR spectra of 3e

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Figure A52: ¹³C NMR spectra of 3e³⁴ Optimization of reaction parameters for formation of 3f Table A32: Optimization table for step one for 3f

Entry Acid (mL) Solvent (%vol)

Temp (°C) Time (min)

1 AcOH (1) - 130 20

2 HCOOH (2) EtOH (50) 150 30

3 HCOOH (2) EtOH (50) 150 90

4 AcOH (1) - 130 90

5 AcOH (1) - 150 30

Table A33: Optimization table for step two for 3f Entry Acid (mL) Solvent

(%vol)

Temp (°C) Time (min) Yield (%)

1 HCOOH - 150 20 -

2 - - - - -

3 - - - - -

4 HCOOH (1) EtOH (75) 130 40 -

5 HCOOH (2) EtOH 100 75 -

3 Carbonyl peak missing possibly due to low concentration. All other data is consistent with the target compound

4 The peak show at around 30 ppm is some unknown impurity that is not part of the structure.

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LC/MS data 1

Figure A53: Chromatogram of step two for 3f Table A34: m/z responses and retention time

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Figure A54: Mass peaks of acid derivative of 3f

Figure A55: Mass peaks of 3f

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2

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3

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4

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5

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REFERENCES

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23. Hassankhani, A. Multicomponent reaction for the synthesis of 2,3- dihydroquinazolin- 4(1H)-ones using isatoic anhydride, aldehydes and NH4OAc catalyzed by SnCl2.2H2O under solvent- free conditions. Iraninan Chemical Journal, 7, Issue 3, 248-256 (2019).

Synthesis of 3,4- dihydroquinazolinones via ring closure or reduction

SYNTHESIS OF 3,4-

DIHYDROQUINAZOLINONES VIA RING CLOSURE OR REDUCTION

Bachelor thesis in Chemistry

by Adam Hallberg

Abstract

TABLE OF CONTENTS

ABBREVIATIONS

INTRODUCTION Overview

The properties of DHQ

Classic methods for synthesis

Modern microwave assisted organic synthesis method

Leuckart reaction

Aim

RESULTS AND DISCUSSION

CONCLUSION

ACKNOWLEDGEMENTS

METHOD AND MATERIALS

Materials

APPARATUS

SOFTWARE

EXPERIMENTAL SECTION

APPENDIX WITH DATA

REFERENCES