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Issue 34, 2015
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Synthesis of chiral hexacyclic steroids via [8π + 2π] cycloaddition of diazafulvenium methides

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Abstract

First examples of [8π + 2π] cycloaddition of 16-dehydropregnenolone (16-DPA) acetate with diazafulvenium methides leading to chiral 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused steroids are reported. These hexacyclic steroids were obtained exclusively or selectively with the approach of the 1,7-dipole by the less hindered α-face of 16-DPA. Quantum chemical calculations at the DFT level were carried out, using the cycloaddition of 1-methyl- and 1-benzyl-diazafulvenium methides with N-phenylmaleimide as model reactions, in order to rationalize the stereochemistry outcome. The results indicate that endo cycloadditions of the more stable dipole conformation, having the 1-substituent pointing outward, are significantly more favorable than the alternative exo cycloaddition.

Graphical abstract: Synthesis of chiral hexacyclic steroids via [8π + 2π] cycloaddition of diazafulvenium methides

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Publication details

The article was received on 03 Jun 2015, accepted on 20 Jul 2015 and first published on 20 Jul 2015


Article type: Paper
DOI: 10.1039/C5OB01110H
Author version available: Download Author version (PDF)
Citation: Org. Biomol. Chem., 2015,13, 9127-9139
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    Synthesis of chiral hexacyclic steroids via [8π + 2π] cycloaddition of diazafulvenium methides

    S. M. M. Lopes, C. F. O. Correia, S. C. C. Nunes, N. A. M. Pereira, A. R. F. Ferreira, E. P. Sousa, C. S. B. Gomes, J. A. R. Salvador, A. A. C. C. Pais and T. M. V. D. Pinho e Melo, Org. Biomol. Chem., 2015, 13, 9127
    DOI: 10.1039/C5OB01110H

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