Cycloaddition of 2-thiazolines and acyl ketenes under acidic conditions results in bicyclic 1,3-oxazinones and not 6-acylpenams as earlier reported

Optically active 2-thiazolines 4 were previously reported to react with acyl Meldrum's acid derivatives 5 under acidic conditions (HCl (g) in benzene) to stereoselectively give 6-acylpenams 1. Rece ...