[3,3]Sigmatropic rearrangement versus [2+2] cycloaddition: A DFT investigation of formal S_N2′ Substitution of imido metal complexes with allylic electrophiles

摘要

Is common sense always best? A DFT investigation of two S _N2′ substitution reactions with different central metals (zirconium and titanium) and types of allylic sources revealed that in both cases, a [2+2]/retro-[2+2] pathway is energetically favorable. This is in contrast with the usually accepted [3,3] sigmatropic rearrangement mechanism (see picture; TMS=trimethylsilyl).