One-stage double methylene transfer reactions from methylsulphinylmethanide to activated double bonds. Mimetic of in vivo C-ethylation

Abstract

One-stage sequential double methylations of the CC bonds in stilbene, 2-methylstilbene, and 4,4′-dimethoxystilbene from methylsulphinylmethanide (DMSO^–) leading to methyl diarylbutyl sulphoxides [e.g.(3) and (14)] are described. The same methyl diarylbutyl sulphoxides are produced when the corresponding α-methylstilbenes [e.g.(6)] or, in one case, the corresponding styrene (5) and lower homologous sulphoxide (4) are similarly treated with DMSO^–; the double methylene transfer process follows according to Scheme 2. Thermal elimination of methanesulphenic acid from the sulphoxides (3) and (14) produces 3,4-diarylbut-1-enes, which are smoothly isomerised by DMSO^– to a mixture of Z- and E-isomers of α-ethylstilbenes and α-benzyl-β-methylstyrenes. Cyclopropane intermediates are shown not to be implicated in any of the reaction schemes by the observation that authentic trans-1,2-diphenylcyclopropane is recovered unchanged after treatment with DMSO^–; the corresponding cis-cyclopropane is quantitatively converted into the trans-isomer in DMSO^––DMSO. (E)-Stilbene reacts with the anion produced from diethyl sulphoxide and sodium hydride to give a mixture of Z- and E-isomers of α-ethylstilbene and α-benzyl-β-methylstyrene. The relationship between this work and in vivo C-ethylation from L-methionine is discussed.