Preliminary Studies on the Michael Addition of Quinones to Nitroolefins: (6bR,10aS)-7,8,9,10,10a,11-Hexahydro-6bH-benzo[a]carbazole-5,6-diones, (4aR,11bS)-1,2,3,4,4a,5-Hexahydro-11bH-benzo[b]carbazole-6,11-diones, and 1,2,3,4-Tetrahydro-5H-benzo[b]carbazole-6,11-diones