Methyl insertion reactions of tetrahydropyrans having a C1'-mesyloxy group on the C2-side chain with trimethylaluminum

Methyl insertion reactions of tetrahydropyrans having a C1'-mesyloxy group on the C2-side chain, mediated by trimethylaluminum, were investigated. Removal of the mesyloxy group, 1,2-hydride shift and/or ring-expansion, and methyl insertion took place concertedly, depending on the stereostructure of the substrate, to give 2-methylated tetrahydropyran and/or 2- or 3-methylated oxepane.