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

Org Biomol Chem. 2015 Sep 14;13(34):9127-39. doi: 10.1039/c5ob01110h. Epub 2015 Jul 30.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Catalysis
  • Cyclization
  • Cycloaddition Reaction
  • Heterocyclic Compounds / chemical synthesis*
  • Imidazoles / chemistry*
  • Indolequinones / chemistry*
  • Models, Molecular
  • Molecular Structure
  • Stereoisomerism
  • Steroids / chemical synthesis*

Substances

  • Heterocyclic Compounds
  • Imidazoles
  • Indolequinones
  • Steroids
  • diazafulvene
  • quinone methide