Synthesis of 6,8-substituted-5,7-difluoro-3,4-dihydro-1H-quinoxalin-2-ones via reductive cyclisation of 2,4,6-substituted-3,5-difluoronitrobenzenes

The synthesis of substituted 5,7-difluoro-3,4-dihydro-1H-quinoxalin-2-ones is described via reductive cyclisation of 2,4,6-substituted-3,5-difluoronitrobenzenes. Reliable conditions for the reduction of solid-phase bound 2,4,6-substituted-3,5-difluoronitrobenzenes were not found. In contrast, solution-phase reductions proceeded smoothly giving the cyclised quinoxalin-2-one products in good yields. A method optimised for rapid parallel synthesis is described, using zinc in acetic acid as reductant, which has been demonstrated to be general for products bearing a range of substituents.