Cyclizations of 2-alkylthiazolines and 2-alkyloxazolines with α,α-disubstituted diacid chlorides or N-(chlorocarbonyl) isocyanate
作者:Aihua Zhou、Charles U. Pittman
DOI:10.1016/j.tetlet.2005.01.146
日期:2005.3
Two-step cyclizations of 2-alkylthiazolines or 2-alkyloxazolines with alpha,alpha-disubstituted diacid chlorides produce excellent yields of 6,6-dialkyl-2,3-dihydrothiazolo[3,2-a]pyridine-5,7-diones and 6,6-dialkyl-2,3-dihydrooxazolo[3,2-ci]pyridine-5,7-diones in refluxing acetonitrile containing Et3N. Similar cyclizations using N-(chlorocarbonyl) isocyanate in place of diacid chlorides produced 2,3-dihydrothiazolo[3,2-c]pyrimidine-5,7-diones or 2,3-dihydrooxazolo[3,2-c]pyrimidine-5,7-diones, respectively. Each cyclization proceeded through cyclic ketene-N,X-acetal (X = O or S) intermediates. (C) 2005 Elsevier Ltd. All rights reserved.