Abstract
A method of convergent and stepwise synthesis of novel 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines using the Weinreb amide group is developed. The cyclization of 4-dimethylamino-1,3-diaza-1,3-butadiene having N-protecting groups (Boc) with N-methoxy-N-methylacrylamide gives 6-unsubstituted 4-dimethylamino-2-phenyltetrahydropyrimidine, which is a synthetic intermediate for 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines. The transformation of the Weinreb amide group to an acyl group via substitution reaction using organolithium reagents, following the elimination of a dimethylamino group using MeI proceeds smoothly, affording 4,6-unsubstituted 5-acyl-2-phenyldihydropyrimidines in good overall yield. The N-protecting group can be easily removed to obtain N-unsubstituted dihydropyrimidines as a mixture of tautomers, and their tautomeric behaviors were analyzed by 1H NMR spectroscopy.
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