Synthesis and Structure of Highly Enantio‐ and Diastereoenriched 1‐Aza‐4‐oxa‐7‐thiabicyclo[3.3.0]octan‐8‐ones Derived from Acyl‐Substituted S‐Benzyl Thiocarbamates

A convenient method for the synthesis of the title compounds 4a,b, 3a,b via an intramolecular condensation of thiourethanes, derived from the acylation of enantioenriched α‐thio benzyllithium compounds, is reported. The structure of one of the major diastereomers was elucidated by a singlecrystal X‐ray analysis and compared to semiempirical calculations.