Hydrogenation Accompanied by Condensation or Cyclization

Similar cyclization at the hydroxylamine may also take place in the presence of a cyano group.154-156 In the hydrogenation of 2-nitro-2 -cyanobiphenyl (27) over platinum oxide in ethanol, 6-aminophenanthridine A-oxide (28) was the sole compound produced. Compound 28, which was suggested to be in equilibrium with 29, was obtained in 90% yield in the hydrogenation in tetrahydrofuran in which 27 was more soluble than in ethanol (eq. 9.65).154 

Hydrogenative cyclization of aromatic nitro compounds at the amino group has been described in a number of examples and widely utilized in the synthesis of five- and six-membered /V-heterocyclic compounds. Walker synthesized 5,6-dimethoxyoxin-dole and 5,6-dimethoxyindole by hydrogenative cyclization of ethyl 4,5-dimethoxy- 

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