380892-92-2Relevant academic research and scientific papers
Facially controlled C-methylation of oxolanyl and cyclopentyl acetate enolates: Application to the total synthesis of (+)-nephromopsinic acid
Mulzer, Johann,Steffen, Ulrich,Martin, Harry J.,Zorn, Ludwig
, p. 1028 - 1043 (2005)
The stereoselectivity of the C-methylation of oxolanyl and cyclopentyl acetate enolates 5a-22a was investigated. The configuration of the C-methyl diastereomers was elucidated by a combination of crystal structure analysis, NMR spectroscopy and chemical correlations. Generally, the methylation proceeded re*-selectively, although with very different degrees of selectivity. The most important stereodirecting effect was a steric one exerted by the 5-phenethyl substituent, and this steric effect was strongly increased by the stereodirecting effect of a 3-OR group. Contrary to previous literature evidence, the endocyclic oxolanyl oxygen does not exert an effect. These findings were applied in a highly stereoselective synthesis of (+)-nephromopsinic acid (94). Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.
