Formation of Seven-Membered Carbocycles by the Use of Cyclopropyl Silyl Ethers as Homoenols

摘要

The presence of heteroatom substituents on cyclopropanes enhances their reactivity toward electrophiles. Ring-opening reactions of cyclopropanols and siloxy derivatives have been extensively investigated.[1] An interesting variation involves the addition of other functionalities (e.g.,vinyl or ethynyl) to cyclopropanols,which offers unique composite groups for theformation of CC bonds.[2,3] The use of a cyclopropanol,which could be viewed as a “homoenol” or “homoenolate”equivalent,in the nucleophilic addition to a carbonyl compound or an acetal,has been limited primarily to 1-alkoxy-1-siloxycyclopropanes.[4] Little was known about the cognate homologous aldol or Mukaiyama reaction of parent cyclopropanols or siloxycyclopropanes.[5,6] We report hereinan expedient entry to seven-membered carbocycles by theKulinkovich cyclopropanation of acetal-tethered esters and asubsequent Lewis acid mediated ring expansion of theresulting cyclopropyl silyl ethers.