ChemInform Abstract: Efficient and Expeditious Protocols for the Synthesis of Racemic and Enantiomerically Pure Endocyclic Enecarbamates from N-Acyl Lactams and N-Acyl Pyrrolidines.

Abstract

A mild, practical, and straightforward protocol for the construction of endocyclic enecarbamates starting from N-acyl lactams and N-acyl pyrrolidines is presented. Lactams were reduced to the corresponding α-hydroxycarbamates in good to excellent yields using DIBAL-H, SuperHydride, or NaBH4 followed by β-elimination (dehydration) promoted by trifluoroacetic anhydride in the presence of hindered nitrogenated bases such as 2,6-lutidine, diisopropylethylamine, or triethylamine. Small variations of this protocol permitted the preparation of several endocyclic enecarbamates (12 examples) in good to excellent overall yields (56−96%). The protocol was demonstrated to be applicable to several ring sizes, compatible with different protecting groups, and to be mild enough to prevent racemization of racemization-prone stereocenters. The efficacy of the procedure in the preparation of enantiomerically pure endocyclic enecarbamates was also demonstrated and compared to the commonly used Shono's protocol, which in our ...