INTRAMOLECULAR CONJUGATE ADDITION-REACTIONS VIA ORGANOZINC COMPOUNDS

This paper describes the application of organozinc compounds in a general strategy for achieving intramolecular conjugate addition with nonstabilized carbanion derivatives. Organozinc iodides, prepared by the reaction of the corresponding organoiodides with activated zinc metal, undergo an intramolecular 1,4-addition reaction with alpha,beta-unsaturated ketones and esters to form five- and six-membered-ring products. A mechanistic study suggests that, at most, only a small part of the cyclization product can result from a radical-mediated pathway. Both olefinic and acetylenic unsaturated carbonyl compounds participate in the intramolecular conjugate addition reaction. Addition of electrophilic reagents such as methyl iodide and acetaldehyde permits the in situ synthetic elaboration of the product enolates.