FORMATION OF HIGHLY SUBSTITUTED CYCLOPENTANES FROM RADICAL AND ANIONIC MICHAEL CYCLIZATIONS OF ALPHA-IODO-GAMMA-LACTONES AND ALPHA-IODO-DELTA-LACTONES

α-Iodo-δ- and -γ-hexonlactones with α,β-unsaturated esters developed from C-6 undergo both tributyltin hydride-induced radical and base catalysed anionic Michael cyclisations to form bicyclic lactones with very highly substituted homochiral cyclopentanes. The δ-lactones give cyclopentane products in which adjacent carbon substituents on the cyclopentane ring are cis to each other, whereas γ-lactones give cyclopentanes in which the carbon chains are trans. © 1994