Syntheses, Substitution and Cyclization Reactions of 7a,8,9,10,11a-Hexahydro-pyrido[3,2,1-jk]carbazoles With a Strychnos Alkaloids Partial Structure

4a-Methyl-2,3,3,4a-tetrahydro-1H-carbazole (3), obtained from phenylhydrazinium chloride and 2-methylcyclohexanone, was regioselectively reduced with sodium borohydride to 4a-methyl-2,3,4,4a,9a-hexahydro-1H-carbazole (4).

Cyclocondensation of hexahydrocarbazole 4 with 2 molecules of diethyl malonate 5a gives 7-hydroxy-13a-methyl-9a,10,11,12,13,13a-hexahydro-5H,8H-pyrano[2',3':4,5] pyrido[3,2,1-jk]carbazole-5,8-dione (6), which affords in a 2-step degradation 5-unsubstituted 4-hydroxy-11a-methyl-7a,8,9,10,11,11a-hexahydro-6H-pyrido[3,2,1-jk]carbazol-6-one (9). Nitration of 9 forms the 5-nitro compound 12, which cyclized after chlorination and azidation at position 4 on thermolysis to the 12a-methyl-7-oxo-8a,9,10,11,12,12a-hexahydro-7H-[1,2,5]oxadiazolo[3',4':4,5]pyrido[3,2,1-jk] carbazol-6-oxide 15.

Cyclocondensation of hexahydrocarbazole 4 with phenylmalonate 5b forms 4-hydroxy-11a-methyl-5-phenyl-7a,8,9,10,11,11a-hexahydro-6H-pyrido[3,2,1-jk]carbazol-6-one (16a), which cyclized after chlorination and azidation at position 4 on thermolysis to the 3b-methyl-3b,4,5,6,7,7a-hexahydroindolo[2',3':4,5]pyrido[3,2,1-jk]carbazol-9(14H)-one derivative 19. The conditions in the thermolytical decomposition and cyclization of the azido compounds were investigated by differential thermal analysis (DSC).