Highly Stereoselective Metal-Free Hydrogenations of Pyrrolo[1,2-a]quinoxalines

A metal-free hydrogenation of pyrrolo[1,2-a]quinoxalines has been successfully realized by using the combination of B(C6F5)(3) and tris(4-methoxyphenyl)phosphine to furnish the corresponding 1,2,3,3a,4,5-hexahydropyrrolo[1,2-a]quinoxalines in 59-99% yields. For 4-aryl-substituted pyrrolo[1,2-a]quinoxalines, high cis selectivities were obtained, but trans-selectivities were achieved for the 4-methyl-substituted substrates.