Synthesis of Carboranylated Dihydropyrrolo[1,2- a ]quinoxalines and Dihydroindolo[1,2- a ]quinoxalines by BF 3 ·OEt 2 -Catalyzed Heterocyclization of C -Formyl- o -carboranes and Investigation of Their Oxidation Stability.

A BF 3 ·OEt 2 -catalyzed synthesis of carboranylated dihydropyrrolo[1,2- a ]quinoxalines and dihydroindolo[1,2- a ]quinoxalines in 30-99% yields is presented through the heterocyclization of various C-modified C -formyl- o -carboranes with 1-(2-aminophenyl)-pyrroles/indoles. A systematic comparative investigation of their oxidation stability in air confirmed that 4-carboranyl-4,5-dihydropyrrolo[1,2- a ]quinoxaline had better stability than the 4-phenyl analogue. A cage-deboronation reaction for N -acetyl-substituted carboranylated dihydropyrrolo[1,2- a ]quinoxaline produced the corresponding 7,8- nido -carborane cesium salt. A kinetic resolution was also realized to obtain an optically pure carboranylated N -heterocycle scaffold bearing a carborane cage carbon-bonded chiral stereocenter.