HFIP-Promoted Divergent Cycloadditions of Difluoroenoxysilanes with 2-Indolylmethanols: Synthesis of Fluoro 2-Pyrano[3,4-]indoles and -Difluoro Cyclopenta[]indoles.

An oxa-6π-electrocyclization of difluoroenoxysilanes with diaryl 2-indolylmethanols has been developed. In addition, a rarely reported C3-nucleophilic [3+2] cycloaddition of difluoroenoxysilanes with dialkyl 2-indolylmethanols has been disclosed. This divergent cycloaddition approach affording readily available difluoroenoxysilanes as three-atom and C2 synthons provides rapid access to fluoro 2-pyrano[3,4-]indoles and -difluoro cyclopenta[]indoles in good to excellent yields with good functional group tolerance. The metal-free and mild conditions using only HFIP as the solvent without any external acid catalyst illuminate practical and environmentally benign advantages.