[2+2] CYCLOADDITION OF ETHYL PROPIOLATE AND SILYL ENOL ETHERS

The [2 + 2] cycloaddition of ethyl propiolate and silyl enol ethers with titanium tetrachloride catalysis gives cy-clobutene adducts. Yields are generally high using tert-butyldimethylsilyl (BuMe2Si) ethers, and correspondingly lower yields were obtained with trimethylsilyl (Me3Si) ethers. The cycloadducts can be opened either thermally or by treatment with acid or base. The overall sequence provides a two-carbon ring expansion which is complimentary to the analogous ring expansion utilizing enamines. Copyright © 1979, American Chemical Society. All rights reserved.