Stereogenic centres, multiple

Rhodium(II) (iV-dodecylbenzenesulfonyl)prolinate has been found to act as an effective catalyst for the enantioselective decomposition of vinyldiazoacetates to c -divinylcyclopropanes. Combination of this process with a subsequent Cope rearrangement has resulted in a highly enantioselective synthesis of a variety of cycloheptadienes containing multiple stereogenic centres (see Scheme 40). The tandem... 

A substantial number of the metabolites isolated still require resolution of stereochemical ambiguities, particularly those examples in which the C-3 acyl groups contain multiple stereogenic centres. A point of interest relates to the isolation of tetramic acid metabolites as salts and whether or not these salts represent the natural form of the metabolites. 

With this procedure ot-alkylated (83), brominated (84), formylated (85), silylated (87 and 89), phosphorylated (88) and hydroxylated (90)198.199 phosphetane oxides have been prepared. Usually the products are present as a single diastereomer, with retention of configuration at the phosphorus atom and with the new substituent installed in the equatorial position, in anti disposition to the menthyl group, as confirmed by X-ray crystallography. Cl- and C2-symmetric phosphetane dioxides or diboranes (88, 89 and 91) have also been obtained. Further elaboration has allowed the preparation of derivatives with multiple stereogenic centres (86). Most of the phosphetane oxides of Scheme 2.30 have been reduced to the parent phosphines... 

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