Titanium-Catalyzed Intermolecular Hydrothiomethylation of Alkenes

A catalyst screening for six different α-alkylation reactions of methyl sulfides with unsaturated substrates performed in hermetically sealable and inexpensive 42-well aluminum reactor blocks is described. As a result, a new titanium-catalyzed hydrothiomethylation reaction of alkenes, which takes place under C─H bond activation at the α-carbon atom of simple methyl sulfides, is presented. The best catalyst is prepared in situ from the readily available titanium catalyst precursor Ti(CH₂SiMe₃)₄, a formamidinato ligand precursor, and the Lewis acid [Ph₃C][B(C₆F₅)₄]. Although selected 1,2-disubstituted alkenes, for example, cyclohexene and cyclopentene, undergo successful hydrothiomethylation reactions, the best results are obtained with monosubstituted 1-alkenes. In these cases, the reactions take place with excellent regioselectivity and give branched hydrothiomethylation products exclusively (23 examples). When dimethyl sulfide is used as a substrate, either the monohydrothiomethylation product or the dihydrothiomethylation product can be obtained with very good selectivity.