A novel route for the preparation of chromenoquinazolines
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A NOVEL ROUTE FOR THE PREPARATION OF CHROMENOQUINAZOLINES O. A. Mazhukina1*, A. G. Platonova1, O. V. Fedotova1, and P. V. Reshetov2 Keywords: 2H-chromen-2-one, chromenoquinazoline, microwave irradiation, Biginelli reaction. It is known that multicomponent reactions involving three or more reagents reacting successively to form a novel product containing the basic structural components of all of the starting molecules are a promising approach for the preparation of heterocyclic compounds. One such method is the Biginelli reaction [1-5]. In this study, 3-(1,3-dioxobutan-1-yl)-2H-chromen-2-one (1), aromatic aldehydes 2a,b, and urea (3) have been used in the Biginelli reaction for the first time. The reaction has been carried out, again for the first time, in both the classical one-pot variation via refluxing in ethanol in the presence of hydrochloric acid, and also solvent-free by 700 Watt microwave irradiation and zinc chloride catalyst. It was found that the nature of the substituent in the aromatic component did not affect the direction of transformation and the yield of the novel, linearly structured condensed systems, namely, 11a-hydroxy4-phenyl- (4) and 11a-hydroxy-4-(4-methoxyphenyl)-4,4a,11a,12-tetrahydro-2H-chromeno[3,2-g]quinazoline2,5(3H)-diones (5). The yield (43-85%) depends on the reaction conditions, reaching the maximum values for the microwave action on the reagent mixture. Formation of compounds 4, 5 points to a Schiff type condensation of the aldehydes 2a,b and urea (3) in the first stage. Without separation, the intermediate is protonated and plays the role of electrophile in attacking the 3-(1,3-dioxobutan-1-yl)-2H-chromen-2-one (1) at the methylene group, to give the adduct A. An intramolecular nucleophilic attack of the carbonyl group by the amino group and carbocyclization of the adduct B gives the stable condensed systems 4, 5. 1 H NMR spectroscopic data suggests that chromenoquinazolines exist in the tautomeric forms 4,4' and 5,5'. The two methine protons on the tertiary carbon atoms appear as multiplets in the regions 2.17-2.72 and 3.58-3.81 ppm respectively, and this is likely associated with the presence of three chiral centers and the possibility of the products occurring in multiple stereoisomeric forms. IR spectra were recorded on an FSM 1201 FTIR spectrometer using KBr pellets. The 1H and 13C NMR spectra were recorded on a Varian 400 spectrometer (400 and 100 MHz, respectively) using DMSO-d6 with TMS as internal standard. Elemental analysis was carried out on a Perkin Elmer 2400 Series II CHNS/O analyzer.
_______ *To whom correspondence should be addressed, e-mail: [email protected]. 1
Chemistry Institute, N. G. Chernyshevsky Saratov State University, 83 Astrakhanskaya St., Saratov 410012, Russia. 2 V. I. Razumovsky State Medical University, 112 Bolshaya Kazachya St., Saratov 410012, Russia; e-mail: [email protected]. _________________________________________________________________________________________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 136
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