I. Zinc-mediated homologation-cyclopropanation in beta-diketones and selectivity within cyclopropanoxide rearrangements. II. Zinc-mediated tandem chain extension-aldol reaction and formation of substituted gamma-lactones

The investigation of homologation-cyclopropanation in beta-diketones revealed the involvement of two donor-acceptor cyclopropane intermediates. Cyclopropanoxide rearrangements were accomplished using reaction conditions other than zinc-carbenoid. Ring fragmentation within chain-extended tertiary cyclopropanoxides was investigated under acidic and basic reaction conditions. Tandem chain extension-aldol reaction and lactonization were accomplished using alpha-carboxyester imides. A diastereomeric mixture of substituted gamma-lactones (cis and trans) was isolated and characterized by NMR studies. Increased diastereomeric ratios of the trans substituted gamma-lactones versus their cis counterparts were attributed towards increased syn-aldol selectivity due to chelation of the zinc-bound ester enolate with the imide carbonyl of the chiral auxiliary.