A synthesis of 3-fluoroindoles and 3,3-difluoroindolines by reduction of 3,3-difluoro-2-oxindoles using a borane tetrahydrofuran complex

A borane tetrahydrofuran complex has been used to study the reduction of 3, 3-difluoro-2-oxindoles and been found to yield either 3-fluoroindoles or 3, 3-difluoroindolines. The latter have been found to be reasonably stable whe n the aromatic nucleus is substituted with an electron withdrawing group an d are in these cases the predominant product. The efficient synthesis of th e former occurs by elimination of HF in the presence of silica from the lat ter. The 3,3-difluoro-2-oxindoles were prepared by the reaction of appropri ately substituted isatin derivatives with DAST. (C) 1999 Elsevier Science L td. All rights reserved.