Conformationally constrained dipeptides. Obtention of enantiomerically pure 6‐acetamido‐5‐oxo‐1,2,3,5,6,7‐hexahydro‐3‐indolizine carboxylic acid

The separation of a stereoisomeric mixture of esters 6, and the synthesis of the new enantiomerically pure unsaturated 6,5‐fused bicyclic lactam 2 are described. The key‐step involves trimethylsilyl iodide cleavage, without racemization, of a vinylogous carbamate. The cis N‐ acetylamino acid 2 is a new scaffold for the synthesis of rigid β‐turn mimetics.