Issue 2, 1974

Conformations of diterpenoids: an X-ray determination of the molecular structure of 6α-bromo-13-hydroxy-14-isopropylpodocarpa-8,11,13-trien-7-one and of the structure and absolute configuration of methyl 6α-bromo-13-isopropyl-7-oxopodocarpa-8,11,13-trien-15-oate

Abstract

The crystal and molecular structures of the title compounds have been determined by X-ray diffraction methods from photographic data by the heavy-atom method; the absolute configuration was established for the second named. Crystals of the former (II) are tetragonal, a= 12·54, c= 23·97, Å, space group P41212; the structure was refined by least squares to R 0·088. The latter (III) is triclinic, a= 6·20, b= 7·73, c= 10·79 Å, α= 97·0, β= 79·3, γ= 104·6°, space group P1; refined to R 0·064. In (II) ring A has a chair conformation with a trans A/B ring fusion; ring B has an approximate boat conformation and the bromine atom has the α-configuration. The bromine is in the same configuration in compound (III) and ring A also adopts the chair conformation. There is trans A/B ring fusion with ring B somewhat distorted but describable as a ‘half-boat’. The stereochemistries at asymmetric centres confirm earlier evidence. There is considerable variation in detailed conformation, however, and a comparison between these compounds and with the molecular structure of methyl 6α-bromo-12-methoxy-7-oxopodocarpa-8,11,13-trien-16-oate leads to the view that steric rather than electronic factors are largely responsible for the path of bromine attack.

Article information

Article type
Paper

J. Chem. Soc., Perkin Trans. 2, 1974, 150-157

Conformations of diterpenoids: an X-ray determination of the molecular structure of 6α-bromo-13-hydroxy-14-isopropylpodocarpa-8,11,13-trien-7-one and of the structure and absolute configuration of methyl 6α-bromo-13-isopropyl-7-oxopodocarpa-8,11,13-trien-15-oate

J. F. Cutfield, T. N. Waters and G. R. Clark, J. Chem. Soc., Perkin Trans. 2, 1974, 150 DOI: 10.1039/P29740000150

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