Phenanthridones reduction

More recently Wege and coworkers synthesized the Nifedipine analogue Af-hydroxy-phenanthridone (50) from Af-benzyloxybiphenyl-2-carboxamide (48) by cyclization to Af-benzyloxyphenanthridone (49) followed by catalytic reductive removal of the benzyl group (Scheme 9). ... 

The characteristic reactions of 6-halogenophenanthridines with nucleophiles have been discussed in Section IV,C (see p. 390), as have the synthetically useful reductive dechlorinations of 6-chloro derivatives (see p. 397). Little attention has been paid to the reactions of other halogenophenanthridines and -phenanthridones. 2-Bromo-phenanthridone (247) can be lithiated with two equivalents of... 

The lithium aluminum hydride reduction of phenanthridones to dihydrophenanthridines is easily accomplished, and has considerable synthetic value90, 134, 211 213 dehydrogenation to the parent bases occurs readily and, unless air is rigorously excluded, may be spontaneous. On treatment with lithium aluminum hydride, followed by acidification, N-methylphenanthridones form the corresponding quaternary salts.211 iV-Phenylphenanthridone gives, in contrast, 5-phenyl-5,6-dihydrophenanthridine.333... 

The reduction of phenanthridine to 5,6-dihydrophenanthridine (90, R = H) was readily accomplished by reaction with lithium aluminum hydride in ethereal solution.118 The same dihydrophenanthridine resulted from the lithium aluminum hydride reduction of 6-chloro-phenanthridine or phenanthridone,1180 thus confirming the position of saturation of the product.119 It is of interest to note that molecular complexes of phenanthridine and dihydrophenanthridine were not observed as products in this reduction as was the case in the metal hydride reduction of phenazine.119... 

Muth et al. studied the hydrogenation and cyclization of 2-nitro-2 -carboxy-biphenyl and its carboxy derivatives (22a-22d) over platinum oxide in ethanol (Scheme 9.13).154 IV-Hydroxyphenanthridone (25) was considered to result from the cyclization at the hydroxylamino compound 23, and phenanthridone (26) to result from the amino compound 24 and not via 25, since 25 did not undergo the reduction to yield phenanthridone under the conditions of the reaction. 

On acid catalysis, 2-aminobiphenyl-2 -carboxylic acids 31 cyclize affording phenanthridones 32, which are reduced by zinc or LiAlH4 to phenanthridines 34. The aminobiphenylcarboxylic acids 31 are accessible from the corresponding nitro compounds 33 by reduction. 

The lithium aluminum hydride reduction of phenanthridones to dihydrophenanthridines is easily accomplished, and has considerable synthetic value dehydrogenation to the parent bases... 

---