Chromium ethylidene

Salzer et al. prepared a set of planar-chiral diphosphine ligands based on the arene chromium tricarbonyl backbone (Fig. 36.3) [21]. The straightforward four-step synthetic route allowed the preparation of 20 ligands of this family. These ligands were tested in Ru- and Rh-catalyzed enantioselective hydrogenation of various substrates, including the standard C=C substrates (dimethyl itaconate, methyl-2-acetamidocinnamate, methyl-2-acetamidoacrylate) as well as MEA-imine (l-(methoxymethyl)ethylidene-methylethylaniline) and ethyl pyruvate. Moderate conversions and ee-values were obtained. 

Several miscellaneous procedures have been reported for the preparation of L-gulonic acid (47). 5-0-Benzoyl-l,3 2,4-di-0-ethylidene-D-glucitol (72) was oxidized388 with chromium trioxide to 73. After hydrolysis of 73, the L-gulose (45) formed was oxidized369,370 with bromine to 21. As noted in Section III,5b, 3,5 4,6-di-0-ethylidene-L-gu-lonic acid (50) was prepared from 3,5 4,6-di-0-ethylidene-D-gulitol (49) in 50-70% yield. By hydrolysis, 50 afforded333 21. 

Pentacarbonyl[l-(phenylthio)ethylidene]chromium(0) is a dark-red, crystalline solid mp 67°. It slowly decomposes in the solid state upon exposure to light. It may be stored for several months at 5° in the dark. It is soluble in aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and other common laboratory solvents such as benzene, 1,4-dioxane, tetra-hydrofuran, chloroform, dichloromethane, and methanol it is slightly soluble in ethanol. In these solvents, solutions of [(CO)5Cr C(CH)3(SC6H5) ] are rapidly decolorized on exposure to light. The infrared spectrum (cyclohexane solution) has v(CO) bands at 2060, 1983, and 1960 cm-1. The nmr spectrum in chloroform-d shows the methyl-proton resonance at t6.71. Other physical properties are reported in the literature.4... 

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