Planar Chirality: Synthesis and Transannular Reactions of Unsaturated Optically Active Azoninones Bearing E-Olefins.

Abstract

The zwitterionic aza-Claisen rearrangement of optically active trans 4-silyloxy-2-vinylpyrrolidines and carboxylic acid fluoride generated nine-membered ring lactams with high yields. The reaction proceeded with an almost complete 1,4-chirality transfer and the exclusive generation of the E-double bond in the medium sized rings to cause additional planar chiral information. The initially formed azoninones were characterized by a pS-arrangement of the olefin with respect to the ring. The rather kinetically stable conformation underwent a flipping of the double bond to give the pR-azoninones as the thermodynamically stable products. The planar diastereomers were subjected to regio- and diastereoselective transannular ring contractions to give indolizidinones. The stereochemical outcome was strongly dependent from the planar chiral information of the double bond and the lactam unit. The so-formed optically active bicycles bearing a defined substitution pattern should serve as versatile building blocks in alkaloid synthesis.