Synthesis of benzofuro[3,2-b]indoline amines via deamination-interrupted Fischer indolization and their unexpected reactivity towards nucleophiles

Abstract

We report the access to the benzofuro[3,2-b]indoline framework of phalarine from benzofuran-2-ones via the Fischer indolization reaction which was interrupted at the deamination step. Unexpectedly, allyl nucleophiles did not add to the aminal position of these benzofuro[3,2-b]indoline amines but to the adjacent ring junction center in the presence of trifluoroborane to deliver 3,3-disubstituted indolines containing a difluoroboron-containing six-membered ring with fluorescence properties.