Locoselective [4 + 2] Cycloadditions of Vinylindoles with Inverse Electron Demand: A new access of indolyl‐substituted and annellated pyridazines

Abstract

Abstract 2‐Vinylindole ( 1a ) and its donor‐ and acceptor‐substituted ( E )‐derivatives 1b – e react highly locoselectively with dimethyl 1,2,4,5‐tetrazine‐3,6‐dicarboxylate ( 3 ) to form the novel (indol‐2‐yl)‐1,4‐dihydropyridazines 4a and 7 as well as the heterocyclic annellated pyridazines 4b , 5 , and 6 . The reactions of the structurally related 3‐vinylindoles 2a – e with 3 also gave rise to new indol‐3‐ylpyridazines 8 , 9 , and 10 . The locoselectivities of these Diels ‐ Alder reactions were controlled mainly by steric effects.