Abstract
Oxidative cyclization of unsaturated Meldrum's acids can be carried out at temperatures as low as −30°C. The rate-determining step is cyclization of the enolate to the alkene (11 to 14 and 15) rather than enolization, which is the rate-determining step with dimethyl 4-pentenylmalonate (1). While cyclization of 1 gives mainly cyclopentanes, cyclization of Meldrum's acids provides a versatile route to cyclohexenes.
Oxidative cyclization of 10 gives primarily cyclohexene 16 by rate-determining cyclization of the Mn(III) enolate of 10 to give a cyclic radical with loss of Mn(II).