Facile synthesis of fully substituted dihydro-β-carbolines via Brønsted acid promoted cascade reactions of α-indolyl propargylic alcohols with nitrones.

A straightforward synthesis of fully substituted β-carbolines via Brønsted acid promoted cyclizations of α-indolyl propargylic alcohols with nitrones is described. The use of nitrones bearing alkenyl or electron-rich aryl groups as the R(4) substituent dramatically switches the reaction pathway to afford tetrasubstituted alkenes and amines, which is assumed to proceed through a rearrangement reaction involving N-O bond cleavage and 1,2-migration of the R(4) group to an adjacent nitrogen atom.