Rhodium-Catalyzed Methylthio Transfer Reaction between Ketone α-Positions: Reversible Single-Bond Metathesis of C−S and C−H Bonds

In the presence of a catalytic amount of RhH(PPh₃)₄ and 1,2-bis(diphenylposphino)ethane (dppe), α-phenylthio ketones were methylthiolated with p-cyano-α-methylthioacetophenone giving α-phenylthio-α-methylthio ketones. The methylthio transfer reaction between the ketone α-positions was reversible and at equilibrium, and the methylthio group was transferred in preference to the phenylthio group. The reaction of tertiary alkyl methylthiomethyl ketones proceeded in high yields; the reaction of diastereomeric 4-(tert-butyl)-2-phenylthiocyclohexanones gave an axial 2-methylthiolated product.