| Popis: |
The flash vacuum pyrolysis (900–940°C) of a series of N-R-substituted carbazole-1,2-dicarboxylic anhydrides (R = methyl, phenyl, o-tolyl, benzyl, and ethyl) leads to 1,2-didehydrocarbazoles which undergo ring expansion, cyclisation, and other reactions but which appear not to undergo ring contraction to exocyclic carbenes. Thus the N-methyl compound 4 gives phenanthridine in 27% yield, the N-phenyl compound 5 undergoes C-2′C-1 cyclisation to indolo[3,2,1-jk]carbazole 27, and the N-o-tolyl compound 6 gives both C-6′C-1 cyclisation and 2′-CH3C-1 cyclisation. The N-benzyl compound 7 mainly suffers loss of the benzyl group, but a minor product, benzo[a]carbazole 33, is probably formed by an intramolecular cycloaddition. The N-ethyl compound 8 forms mainly carbazole and phenanthridine and in addition the minor C-2′C-1 cyclisation products pyrrolo[3,2,1-jk]carbazole 44 and its 4,5-dihydro derivative 45. The formation of phenanthridine from the N-methyl anhydride 4 has been investigated by labelling of 4 with 13C at C-9a. |
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