AgNO3·SiO2: Convenient AgNPs source for the sustainable hydrofunctionalization of allenyl-indoles using heterogeneous catalysis

Abstract

Supported silver nitrate in silica gel has been demonstrated as an excellent heterogeneous catalytic system for the selective hydroarylation of indole-tethered allenes, with a selectivity reversal in comparison with homogeneous gold catalysis. In this way, the controlled preparation of 1,2-disubstituted-9H-carbazoles, 1,2-disubstituted-4,9-dihydro-1H-carbazoles, and 2,4-disubstituted-spiro[cyclopentane-1,3′-indol]-3-enes has been accomplished. Control experiments supported by Density Functional Theory calculations strongly suggest that indole-tethered allenes react through a 5-endo-dig-carbometallation/rearrangement sequence, which contrasts to the previously reported 6-endo-dig-carbometallation pathway promoted by [Au(I)]-catalysts in related systems.