ITERATIVE SYNTHESIS OF SELECTIVELY SUBSTITUTED ALPHA,BETA-UNSATURATED AND SATURATED MEDIUM-RING LACTONES

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 l-[(trimethylsilyl)oxy]-2-chlorobicyclo-[n,1.0]oxanes. Thermal rearrangement of these adducts led to the a,0-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. © 1990, American Chemical Society. All rights reserved.