A highly selective Bi(OTf)3 mediated fragmentation-contraction of δ-ortholactones. A facile route to functionalized γ-lactones

A very selective method for the formation of gamma-lactones from pyranyl ortholactones has been developed which occurs via a fragmentation-acetate migration-ring contraction process. The reaction is very functional group tolerant, providing functionalized gamma-lactones as a single isomeric product following the ring contraction. Mechanistic studies indicate the reaction is mediated by triflic acid liberated from Bi(OTf)(3) in a slow and controlled manner providing excellent chemo and regioselectivity. We propose the triflic acid acts as both a proton and a nucleophile source with triflate anion mediating the fragmentation process. (C) 2018 Elsevier Ltd. All rights reserved.