[reaction: see text] The first example of a kineticresolution process promoted by electrophilic selenium reagents is reported. Racemic allylic alcohols react with half equivalents of a selenenylating agent in methanol leading to the regiospecific formation of the corresponding addition products with a very high level of facial selectivity (from 95:5 to 98:2 dr). The unreacted alcohols can be recovered
The substratespectrum of the inverting alkylsulfatase Pisa1 was investigated using a range of sec‐alkyl sulfate esters bearing aromatic, olefinic and acetylenic moieties. Perfect enantioselectivities were obtained for substrates bearing groups of different size adjacent to the sulfate ester moiety. Insufficient selectivities could be doubled by using dimethyl sulfoxide (DMSO) as co‐solvent. Hydrolytically
Diastereotopos-differentiating allylic alkylation as a key step in the synthesis of γ-glutamyl boletine
作者:Dnyaneshwar Gawas、Uli Kazmaier
DOI:10.1039/b917589j
日期:——
γ-glutamyl boletine is described, based on a diastereotopos-differentiating allylic alkylation of chelated amino acidesterenolates. Independent of the configuration of the leaving group in the allylic substrate, the allylation product is obtained as a single stereoisomer. Its configuration is solely controlled by the stereogenic center adjacent to the π-allyl complex formed.
an efficient catalytic system for the enantioselectiveaddition of alkyl Grignard reagents to a broad range of aliphatic aldehydes with good yields and enantioselectivities. Remarkably, the challenging methylmagnesium bromide (MeMgBr) can also be added to a variety of aliphatic aldehydes, providing versatile chiral methyl carbinol units with unprecedented yields and enantioselectivities in a simple
An efficient reductive Claisen rearrangement, catalyzed by in situ generated copper hydride and stoichiometric in diethoxymethylsilane, has been developed. Yields of up to 95 % with good to excellent diastereoselectivities were observed in this reaction. Mechanistic studies showed that the stereospecific rearrangement proceeded via a chair transition state of (E)‐silyl ketene acetals as intermediates