Planar chirality: Synthesis and transannular reactions of unsaturated optically active azoninones bearing E-olefins

The zwitterionic aza-Claisen re arrangement of optically active trans 4-sil yloxy-2-vinylpyrrolidines and carboxylic acid fluoride generated nine-membe red ring lactams with high yields. The reaction proceeded with an almost co mplete 1,4-chirality transfer and the exclusive generation of the E-double bond in the medium sized rings to cause additional planar chiral informatio n. The initially formed azoninones were characterized by a pS-arrangement o f the olefin with respect to the ring. The rather kinetically stable confor mation underwent a flipping of the double bond to give the pR-azoninones as the thermodynamically stable products. The planar diastereomers were subje cted to regio- and diastereoselective transannular ring contractions to giv e indolizidinones. The stereochemical outcome was strongly dependent from t he planar chiral information of the double bond and the lactam unit. The so -formed optically active bicycles bearing a defined substitution pattern sh ould serve as versatile building blocks in alkaloid synthesis.