Stereoselective synthesis of chiral polyfunctionalized cyclohexane derivatives. Palladium(II)-mediated reaction between cyclohexenones and diazomethane

Several chiral polyfunctionalyzed cyclohexanones and cyclohexenones have been synthesized through Diels–Alder cycloadditions, stereoselectivity being stated by X-ray structural analysis and NOE experiments. The chemoselectivity in the palladium(II)-catalyzed reaction between cyclohexenones and diazomethane has been investigated. Thus, in those enones bearing an amide function on the γ-carbon, the preferential addition occurs at the carbonyl giving epoxides which, under acid conditions, rearrange to tetrahydrobenzoxazoles. The other cyclohexenones afford cyclopropanes as a result of addition to the CC bond. A mechanistic approach to explain the whole process is proposed.