Construction of Halofunctionalized Indenes via a Cascade Prins‐Nazarov Cyclization Promoted by Dual Roles of BX3

Abstract Halofunctionalization of various unactivated arylalkynes to the corresponding 1H ‐indenes in the presence of a particular class of carboxaldehydes and boron trihalides (BX 3 , X=F, Cl, Br, I) is described. A diverse array of halofunctionalized indenes substituted with a heterocycle has been synthesized regioselectively with BX 3 as a promotor for the carbocyclization and a source of X − for halogenation. This reaction proceeds via a formal halogenative [4+1] cycloaddition between arylalkynes and carboxaldehydes promoted by boron trihalides to generate halofunctionalized indenes. The usefulness of the halofunctionalized indenes was demonstrated by their conversion to other derivatives via coupling, nucleophilic substitution, and oxidation. magnified image