Lithiation of 1-alkynyl-1-chlorocyclopropanes and subsequent reactions with electrophilic reagents: synthesis of functionalized alkynyl- and vinylidenecyclopropanes

Abstract

1-Alkynyl-1-chlorocyclopropanes undergo chlorine-lithium exchange on treatment with BuⁿLi in THF at -40—0 °C. Thus generated organolithium species react with carbon dioxide (dry ice) and acetone to give selectively hitherto unknown 1-alkynylcyclopropanecarboxylic acids and the corresponding alcohols in up to 74% yields. Similar reactions involving methyl chloroformate result in the mixtures of cyclopropylacetylenic and vinylidenecyclopropanic esters, while the use of aliphatic aldehydes as electrophiles provides secondary allenic alcohols in up to 64% yields.