Treatment of (R)-[{α-(dimethylamino)ethyl}-η6-benzene]Cr(CO)3 with esters of chloroformic
acid leads to stereoselective substitution of the dimethylamino group for a chloro substituent.
The reaction can be extended to systems in which the chromium arene complex, after
metalation, is diastereoselectively substituted in the ortho position with carbon and silicon
electrophiles to generate planar chirality. The chloro group in turn can be replaced
stereoselectively for various phosphorus, nitrogen, and oxygen nucleophiles. Both substitution
reactions in the benzylic position proceed via retention of configuration. The addition of
cyanide is not stereospecific. The phosphine derivatives are efficient catalysts for the
enantioselective hydrovinylation of styrene to 3-phenyl-1-butene. X-ray crystal structures
establish the absolute configuration of (R)-[(α-chloroethyl)η6-benzene]Cr(CO)3, (R)-[{α-(diphenylphosphanyl)ethyl}-η6-benzene]Cr(CO)3, and (pS,S)-[1-(α-cyanoethyl)-2-methyl-η6-benzene]Cr(CO)3.
Synthesis of KDO Using Indium-Mediated Allylation of 2,3:4,5-Di-Oisopropylidene-D-arabinose in Aqueous Media. -A short, new route to 3-deoxy-D-manno-2-octulosonic acid (KDO) (VI), which is complementary to existing enzymatic and nonenzymatic methods of KDO-synthesis, is based on the In-mediated allylation of protected D-arabinose (I). -(GAO, J.; HAERTER, R.; GORDON, D. M.; WHITESIDES, G. M.; J.
1993 stereochemistry stereochemistry (general, optical resolution) O 0030 24 -066 Synthesis of Chiral Cobalt Complexes with Planoid-Tetradentate Ligand System.-Cobalamins and related derivatives are versatile, enantioselective catalysts for electron transfer induced reactions. Since cobalamins can act in the reaction of achiral educts only in the direction of one enantiomorphous form, synthetic B12-analogous metal complexes are needed, which are accessible in both enantiomorphous forms. As model compounds Co complexes (I) and (II) are chosen which contain a chiral tetradentate-planoid ligand system consisting of two different parts. A study on the catalytic properties of (I) in the isomerization of the achiral 1,4-epiperoxide (III) shows a high activity, but (IV) is obtained only as a racemic mixture. When using (II) as the catalyst, the change in the ligand periphery causes the generation of (IV) with an excess of the (S) enantiomer. The catalytic activity is comparable to that of vitamin B12. -(HAERTER, R.; WEYMUTH, C.; SCHEFFOLD, R.; ENGEL, P.; LINDEN, A.; Helv. Chim. Acta 76 (1993) 1, 353-371; Inst. Org. Chem., Univ. Bern, CH-3012 Bern, Switz.; DE)
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