Design of New Calcium Antagonists. 4‐Aryl‐1,4‐Dihydropyrimidine‐5‐Carboxylates from Olefinic Acetoacetic Esters and Amidine via Regiospecific Ring Closure [1

Abstract

Abstract5‐Functionalized‐l,4‐dihydropyrimidines (5) were prepared via a twostep reaction between arylidene acetoacetic esters (1) and amidines (2). Intermediate 6‐hydroxytetrahydropyrimidines (4) were isolated under mild conditions, and subsequently dehydrated by heating in glacial acetic acid. Warming a solution of 1a and 2a, without isolation of the intermediate product, afforded 5‐acetyl‐6‐oxo‐1,4,5,6‐tetrahydro‐pyrimidine (3), indicating ring closure via the α,β‐unsaturated ester fragment of 1. The mechanism of formation and structure of cyclic adduct intermediates 4, and final dihydropyrimidines 5 are discussed.