High regioselectivity in the heterocyclization of β-oxonitriles to 4-oxothiazolidines: X-ray structure proof

Base-catalyzed reactions of β-oxonitriles with diethyl mercaptosuccinate favour heterocyclization to afford 2-alkylidene-4-oxothiazolidines , rather than 2-alkylidene-4-oxo-1,3-thiazinanes . The observed regioselectivity is based on spectroscopic and experimental evidence, including a single-crystal X-ray structure determination.