| Autor: |
Lopes SM; Centro de Química de Coimbra, Department of Chemistry, University of Coimbra, 3004-535 Coimbra, Portugal. tmelo@ci.uc.pt., Correia CF, Nunes SC, Pereira NA, Ferreira AR, Sousa EP, Gomes CS, Salvador JA, Pais AA, Pinho e Melo TM |
| Jazyk: |
angličtina |
| Zdroj: |
Organic & biomolecular chemistry [Org Biomol Chem] 2015 Sep 14; Vol. 13 (34), pp. 9127-39. Date of Electronic Publication: 2015 Jul 30. |
| DOI: |
10.1039/c5ob01110h |
| Abstrakt: |
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. |
| Databáze: |
MEDLINE |
| Externí odkaz: |
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