62859-36-3Relevant academic research and scientific papers
Steric Effects on Oxymercuration: Oxymercuration-Demercuration of Taraxasteryl, Pseudo-Taraxasteryl, and 19-Epi-Taraxasteryl Acetates
Majumder, P. L.,Laha, S.
, p. 548 - 554 (2007/10/02)
Contrary to usual expectation, taraxasteryl acetate (1b) and pseudo-taraxasteryl acetate (2b) were found to be totally intensive to normal oxymercuration.This has been rationalised as being due to the steric effects of the 19-and 17 methyl groups on the formation of intermediate mercurium ions, and on the nucleophile attacking these species.Conformational analysis of 1b shows that its ring E is not a normal chair, but assumes a twisted conformation due to severe nonbonded interaction between the 12-methylene and the 19-methyl group.Both 1b and 2b, however, underwent oxymercuration-demercuration with allylic rearrangement to give the same compound 2c, when heated with Hg(OAC)2 in glacial HOAc.A partial synthesis of 19-epi-taraxasteryl acetate (1d) has been achieved by Wittig reaction on the 19-epi-norketone (4b) formed by base-catalysed epimerization of 4a which in turn was derived from 1b.The steric effects providing the driving force for this unconventional epimerisation of 4a to 4b have been explained and supported by comparative 13C nmr spectral analysis of 4a and 4b.Unlike 1b and 2b, 19-epi-taraxasteryl acetate (1d) undervent normal oxymercuration.The stereochemical aspect of this reaction has been discussed.
Molecular Rearrangement: Part II - Acid-catalysed Transformation of Taraxasteryl Acetate Epoxide
Ganguly, J. K.,Som, U. K.,Haque, K. E.,Dhara, K. P.,Dutta, C. P.
, p. 1065 - 1066 (2007/10/02)
Taraxa-20α,30α-oxido-3β-yl acetate (I) on treatment with boron trifluoride etherate in dry benzene furnishes taraxa-30-al-3β-yl acetate (II) along with an interesting keto acetate (III) having an enlarged ring-E.I reacts with dry hydrogen chloride in chloroform to yield taraxa-21-oxo-3β-yl acetate (V) and a chlorine incorporated product, taraxa-30-chloro-20(21)-en-3β-yl acetate (VI).However, aqueous perchloric acid treatment of I yields only V.
