BF3.OEt2 catalysed synthesis of diverse 9‑fluorenlidene appended indole-1-oxides and spiro[fluorene-9,10′-indeno[1,2-b]indol]-5′-yl) ethanones from 9-(phenylethynyl)-fluoren-9-ol and nitrosobenzene

Abstract

• A highly efficient approach for the construction of the 9‑fluorene appended 3 H -indole- N -oxide derivatives and spiro difluorene derivatives from fluorine propargylic alcohols and nitrosobenzene catalyzed by BF 3 .OEt 2 has been developed. • The formation of title compounds depends on the mole equivalent of fluorine propargylic alcohol. • A plausible mechanism for the formation of title compounds via an allenenyl cation intermediate is provided. • Single-crystal XRD method was used to unravel the structure of representative compounds.