Ene-hydrazide from enol triflate for the regioselective Fischer indole synthesis.

Ene-hydrazide prepared from enol triflate undergoes a Fischer indolization reaction to give the corresponding indole with complete regioselectivity. The starting enol triflate is readily accessed in regiochemically defined form from the ketone precursor via various well-established methods. This new protocol was successfully applied to the synthesis of desbromoarborescidine A, a natural β-carboline alkaloid, difficult to prepare with conventional Fischer indole synthesis.