Catalytic Amidomethylative [2+ 2+ 2] Cycloaddition of Formaldimine and Styrenes toward N-heterocycles

Abstract

Chemo-switchable catalytic [2+2+2] cydoaddition of alkenes with fomialdimines is reported. Bis(tosylamido)methane (BTM) and 1,2-ditosyl-1,2-diazetidine (DTD), two bench-stable precursors for highly reactive tosylformaldimine, have been identified to be effective. BTM worked as a selective releaser of the formaldimine for catalytic [2+2+2] reactions toward hexahydropyrimidine products via a presumable 'imine-alkene-imine' addition. A unique catalytic retro-[2+2] reaction of DTD was used and has enabled a proposed 'imine-alkene-alkene' pathway with high chemoselectivity for the synthesis of 2,4-diarylpiperidine derivatives. The two alternative processes are catalyzed by the simple and environmentally benign catalysts InCl3 and FeBr2, respectively.