Cross-coupling of 4,5,6,7-tetrahydroindole with functionalized haloacetylenes on active surfaces of metal oxides and salts

Abstract

Screening was performed of metal oxides (MgO, CaO, ZnO, BaO, Al2O3, TiO2, ZrO2) and salts (CaCO3, K2CO3, ZrSiO4) as active surfaces for the reaction of ethynylation of 4,5,6,7-tetrahydroindole with ethyl bromopropynoate and bromobenzoylacetylene. It was established that Ca, Mg, Zn, and Ba oxides assist the ethynylation of 4,5,6,7-tetrahydroindole, and their activity in the reaction with ethyl bromopropynoate considerably exceeds that of aluminum oxide. The ethynylation is accompanied with the formation of intermediate E-2-(1-bromoethenyl)-4,5,6,7-tetrahydroindole and side 1,1-di(4,5,6,7-tetrahydroindol-2-yl)ethenes and 1,1-di(4,5,6,7-tetrahydroindol-2-yl)bromoethanes.