Transition metal-free C(sp3)–H bond coupling among three methyl groups
A coupling of multiple C(sp3)–H bonds of the methyl group in methyl ketones with dimethyl sulfoxide is developed. This coupling allows the direct C(sp3)–H bond coupling among three methyl groups and affords one C–C bond and one CC bond under transition metal-free conditions. The value-added cyclized 3-methylthiomethyl chroman-4-ones can be synthesized through this method. A plausible mechanism is proposed.