Generation of Cyclic Ketene-<i>N</i>,<i>X</i>-Acetals (X = O, S) from 2-Alkyl-1,3-oxazolines and 2-Alkyl-1,3-thiazolines. Reactions with Acid Chlorides, 1,3-Diacid Chlorides and<i>N</i>-(Chlorocarbonyl) Isocyanate

Abstract

2-Alkyl-1,3-oxazolines, 2-alkyl-1,3-thiazolines, and the corresponding cyclic ketene-N,X-acetals (X = O, S) derived from them were reacted with monoacid chlorides, diacid chlorides, tri­acid chlorides. A series of these carbon-carbon bond-forming reactions and cyclizations to both substituted 2,3-dihydrooxazolo[3,2-a]pyridine-5,7-diones and 2,3-dihydrothiazolo[3,2-a]pyridine-5,7-diones proceeded under mild reaction conditions. Cyclic ketene-N,X-acetal intermediates play important roles in all these reactions. Related cyclizations with N-(chlorocarbonyl) isocyanate formed substituted 2,3-dihydrooxazolo[3,2-c]pyrimidine-5,7-diones and 2,3-dihydrothiazolo[3,2-c]pyrimidine-5,7-diones.