Synthesis of mitomycin C analogs. 2. Introduction of a leaving group at C-1 and oxidation of the aromatic ring in 2,3,9,9a-tetrahydro-1H-pyrrolo[1,2-a]indoles

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Abstract

2“(2, 5-Dihydro-1H-pyrrol-1-yl)-α-(phenylmethylene)benzeneacetonitriles 6a, b cyclize thermally in aprotic solvents to the cis- and/or trans-9, 9a-dihydro-3H-pyrrolo[1, 2-a]indoles Ta, 8a and 7b, 8b, respectively. Reaction in methanol affords the 2-(1H-pyrrol-1-yl)benzeneacetonitriles 9a, b as the main products. The appropriate double bond in 8a, b reacts with osmium tetraoxide to give exclusively the cis-vicinal diols 15 and 13, respectively. The stereochemistry of the former has been determined with single-crystal X-ray analysis. The (4, )5-substituted-α-(phenylmethylene)-2-(1-pyrrolidinyl)benzeneacetonitriles 6d-f react in refluxing 1-butanol to give mixtures of the corresponding cis- and trans-(6, )7-substituted-2, 3, 9, 9a-tetrahydro-1H-pyrrolo[1, 2-a]indoles 22b-d and 23b-d, respectively. The rate of cyclization is dependent on the nature of the substituents. Nitration of 22c, 23c affords the 5-nitro-1H-pyrrolo[1, 2-a]indoles 25a and 25b, respectively, in low yield. The corresponding 8-nitro-1H-pyrrolo[1, 2-a]indoles 28a, b are prepared via cyclization of the appropriate 6-nitro-α-(phenylmethylene)-benzeneacetonitriles 27. Reduction of 25a, b and 28a and subsequent oxidation of the corresponding anilines 25c,d and 28c with Fremy's salt do not give the desired p-quinones; in the case of 25a, b a 9H-pyrrolo[1, 2-a]indole (29) is isolated.

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