Use of Protected β-Bromocyclopentenones and β-Bromocyclohexenones as β-Acylvinyl Anion Equivalents

Article abstract of DOI:10.1021/jo00136a001

Ethylene glycol ketals of the 3-bromocyclohex-2-en-1-one as well as its 2-methyl, 2-n-propyl, and 5,5-dimethyl derivatives have been prepared, and their reactions with butyllithium were studied.The organolithium reagents derived from the above compounds react with a variety of electrophiles to afford after acid hydrolysis the corresponding 3-substituted cyclohexenones.Attempts to prepare the ethylene glycol ketal of 2-methyl-3-bromocyclopent-2-en-1-one gave a low yield of the bromoketal.However, dithioketals of 3-bromocyclopent-2-en-1-one and its 2-methyl derivativecould be prepared in good yield.The metalation chemistry of the dithioketals in both the five- and six-membered-ring series was examined.The functionalization chemistry of the resulting organolithium compounds afforded after dithioketal hydrolysis 3-functionalized cyclohex-2-en-1-ones and cyclopent-2-en-1-ones.Several limitations of the chemistry using allyl bromide and cyclohexenone as electrophiles are noted.