Enantioselective construction of spiro{cyclopropane-14′-bicyclo[3.3.0]oct-1-en-3-ones}

Abstract

Intramolecular Pauson-Khand reactions of 1,6-enynes 3a–c with a methylenecyclopropane terminator and a chiral acetal moiety adjacent to the triple bond gave spiro{cyclopropane-1,4′-bicyclo[3.3.0]oct-1-en-3-ones} 5a–c in good yields with a diastereoselectivity of up to 6.4:1. The major diastereomer of 5b was converted to enantiomerically pure bicyclo[3.3.0]octane-3,8-dione 8, which showed a negative peak at 287 nm in the CD curve, consistent with an assumed (5 R) configuration.