Novel domino reactions in β-carbolines with triple bonded dienophiles

Vinylpyrrolo-[2,1-a]-β-carbolines 1 give different products upon reaction with dienophiles. With dimethyl acetylenedicarboxylate (DMAD), a novel domino process takes place, involving Michael attack and rearrangement, affording complex polycycles like 3, 4, and 5. Diels–Alder cycloadditions are favored in the presence of Lewis acids and are the only reactions with dimethyl maleate. When 3-butyn-2-one is used as dienophile, a Stevens rearrangement is observed giving product 9.