Regiocontrolled Synthesis of Mono-, Di, and Trisubstituted Cyclohexenones by Cycloaddition of Vinyl Sulfones to 1-Methoxy-3--1,3-butadienes. Conversion of Alkenes into Effective Dienophilic Reagents

Article abstract of DOI:10.1021/jo00173a040

Cycloaddition of phenyl vinyl sulfone to Danishefky's diene followed by direct ketalization provided 7, a synthon for the 4-(2-cyclohexenyl) anion.Thus, 7 readily undergoes regiospecific γ-alkylation.Ensuing reductive desulfonylation and hydrolysis provides 2-(and 3-)-cyclohexenones efficiently.Zingiberenol, a monocyclic sesquiterpene, was prepared by means of this methodology.Terminal alkenes and cyclic olefins enter into comparable regiocontrolled Diels-Alder addition if they are first subjected to selenosulfonation and oxidation to the vinyl sulfone.Removal of the phenylsulfonyl substituent after condensation provides the adducts which are formally derived from alkylation of the hypothetical C₅ anion of 2-cyclohexenone.The scheme can be expanded to include γ-alkylation prior to desulfonylation.By this means, one is able to prepare 4,5-disubstituted 2-(and 3-)cyclohexenones where the nature of the pendant side chains can be widely varied.