Novel redox cyclisation products derived from 2-acylpyrroles and trans-3-bromo-3,4-dihydro-4-hydroxy-2,2-dimethyl-2H-chromene-6-carbonitrile

Abstract

The reaction of 2-(trifluoroacetyl)pyrrole with trans-3-bromo-3,4-dihydro-4-hydroxy-2,2-dimethyl-2H-chromene-6-carbonitrile under basic conditions has been shown to afford high yields of (4R*, 5aS*,11 bS*)-5a-hydroxy-6,6-dimethyl-4-trifluoromethyl-5a,11 b-dihydro-4H,6H-pyrrolo[1′,2′:4,5]-oxazino[2,3-c]chromene-10-carbonitrile rather than the anticipated amino alcohol. The unequivocal structural assignment of this unusual tetracyclic product by spectroscopic and X-ray crystallographic techniques is described and possible mechanistic explanations for its formation are discussed. Analogous reactions of pyrroles substituted in the 2-position by formyl, acetyl and benzoyl moieties have been shown to behave in an essentially similar manner, suggesting that the reaction is general for 2-acylpyrroles.