REACTIVITY OF HEXAHYDROCARBAZOL-4-ONES IN MICHAEL REACTIONS - STEREOCONTROLLED FORMATION OF DECAHYDROPYRIDO[2,3-D]CARBAZOLES

The reactivity of hexahydrocarbazolones 3 and 7 in Michael reactions h as been studied with several reagents: treatment with acrylonitrile, m ethyl acrylate and the Mannich base of methyl vinyl ketone leads to Qa -substituted compounds 13-16 in good yields (65-93%), as previously ob served with nitroethylene. In contrast, unexpected tetracyclic carbazo les 17 and 18 are obtained with methyl vinyl ketone itself. Reductive cyclisation (H-2, PtO2) of 4a-cyanoethylhexahydrocarbazolones 13 and 1 5 affords decahydro-pyrido[2,3-d]carbazoles 20 and 21, potential inter mediates in the synthesis of E-homo Aspidosperma alkaloids. Compounds 20 and 21 are isolated as single diastereoisomers with a CIE trans rin g junction.dagger