Iterative Synthesis of Selectively Substituted α,β-Unsaturated and Saturated Medium-Ring Lactones

Article abstract of DOI:10.1021/jo00303a010

Chloro, chloromethyl and chlorofluoro carbenoids, generated by reaction of a base on the corresponding halides, were added to trimethylsilyl enol ethers derived from lactones, to give 1-<(trimethylsilyl)oxy>-2-chlorobicyclooxanes.Thermal rearrangement of these adducts led to the α,β-ethylenic lactones, corresponding to a one-carbon ring expansion of the starting lactones.After hydrogenation, with the same iterative sequence a new one-carbon ring expansion could be performed.This method allowed the preparation in good yields of hitherto unknown medium-ring lactones.Spectroscopic and physicochemical properties of the isomeric unsaturated lactones were examined.For the 9- and 10-membered series, the trans isomers could be readily isomerized by I2 into the cis isomers or gave diolides under acidic conditions.