Steric control based on alkyl substituents in the [2,3]sigmatropic rearrangement of nine-membered allylsulfonium ylides. A new entry to the stereoselective synthesis of elemane-type sesquiterpenoids

Abstract

The rhodium(II)-catalysed cyclisation of acyclic α-diazomalonate 1b and α-diazo-β-keto esters 1c, d give stereoselectively the highly substituted δ-lactone 3b and cyclohexanones 3c, d, respectively, by [2,3]sigmatropic rearrangement via the stereocontrolled nine-membered allylsulfonium ylides 2b–d.