Regioselective synthesis of mono- and bis-decahydrobenzocarbazoles via tandem reactions of α-diazo ketones

Regioselective intermolecular 1,3-dipolar cycloaddition reactions of rhodium generated carbonyl ylides with indoles are reported in this paper. Intermolecular 1,3-dipolar cycloaddition reactions of five-membered-ring cyclic carbonyl ylides with indole and substituted indoles afforded hexahydro-2H-carbazol-2-ones in a regioselective manner. Similarly, reactions of cyclic carbonyl ylides were carried out to afford decahydrobenzo[c]carbazoles or decahydrocyclopenta[c]carbazoles with high regioselectivity. Interestingly, the other possible regioisomer decahydrobenzo[a]carbazoles were also obtained by the reaction of cyclic carbonyl ylides and indoles having electron withdrawing substituents. The structure and stereochemistry of regioisomers 6,11c-epoxy-1,2,3,4,4a,5,6,6a,11b,11c-decahydro-4a-methyl-5-oxo-7H-benzo[c]carbazole and 11-benzenesulfonyl-6,11b-epoxy-2,3,4,4a,5,6,6a,11,11a,11b-decahydro-4a-methyl-5-oxo-1H-benzo[a]-carbazole were unequivocally corroborated by single-crystal X-ray analyses. To advance this study, regioselective double 1,3-dipolar cycloaddition reaction of five-membered-ring cyclic carbonyl ylides has been demonstrated for the first time with biindoles having various aryl and alkyl spacers. This process constructed up to eight stereocenters, four carbon-carbon and two carbon-oxygen bonds in a single step with an excellent molecular complexity and stereoselectivity. (C) 2004 Elsevier Ltd. All rights reserved.