Catalytic Asymmetric Diels-Alder Reaction/[3,3] Sigmatropic Rearrangement Cascade of 1-Thiocyanatobutadienes.

A highly efficient asymmetric Diels-Alder/[3,3] sigmatropic rearrangement reaction of methyleneindolinones with 1-thiocyanatobutadienes has been realized by using a chiral N,N'-dioxide/nickel(II) complex as the catalyst. A range of cyclohexenyl isothiocyanates were synthesized in high yields with excellent diastereo- and enantioselectivities. Based on mechanistic studies, a catalytic cycle with possible transition-state models were proposed to explain the process.