Nitroindole condensation

An Organic Syntheses preparation of 4-nitroindole may involve a related reaction. The condensation occurs in the presence of diethyl oxalate which may function by condensation at the methyl group. If this is the case, it must subsequently be lost by deacylation[17]. 

Substitution for PABA in a FA analogue by an indole ring has been accomplished by a Russian group Scheme 3.159) [290], Thus, acylation of dimethyl glutamate with 5-nitroindole-2-carbonyl chloride followed by catalytic hydrogenation furnished (701) which was condensed with (11) to yield imine (702). This was reduced with sodium borohydride to give (703) uneventfully. 

Thus, the suitably constrained benzoxacine derived phenylhydrazine 84 was prepared and condensed with 4-benzyloxybutanal to provide the hydrazone 85. Heating 85 in acetic acid with a slight excess of 5-sulfosalicylic acid afforded the indole 86. The dimethylene tether was subsequently removed by treatment with base (NaOEt, DMSO) followed by acidification to afford the desired product, 7-hydroxy-4-nitroindole. 

Availability of nitroarenes and anilines opens almost unlimited simple and efficient access to phenazines, as well as to their derivatives condensed with an additional ring, as exemplified by the synthesis of pyrrolo[3,2-h]phenazine from 5-nitroindoles (Scheme 99) [234]. 

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