Arene-Cr , complex

Fomarini and colleagues gave also experimental evidence that in the reaction of trime-thylsilicenium ion with arenes, cr-complexes such as 54 are produced29-31. The kinetic isotope effect of the gas phase deprotonation reaction and specific deuterium labeling... 

In a similar manner, asymmetric carbonyl olefination of meso-dicarbonyl compounds was extended to metallic arene or diene complexes [37], such as // -diene Fe or // -arene Cr complexes, to form planar complexes with high enantiomeric bias (Scheme 7.8). Since both complexation and decomplexation of these optically active compounds occur readily, these olefinic complexes are effective as stereocontrollers due to the presence of bulky metal tricarbonyl groups, and serve as useful reactants for obtaining optically active compounds of central chirality by appropriate chemical transformation. 

Due to the inherent unsymmetric arene substitution pattern the benzannulation reaction creates a plane of chirality in the resulting tricarbonyl chromium complex, and - under achiral conditions - produces a racemic mixture of arene Cr(CO)3 complexes. Since the resolution of planar chiral arene chromium complexes can be rather tedious, diastereoselective benzannulation approaches towards optically pure planar chiral products appear highly attractive. This strategy requires the incorporation of chiral information into the starting materials which may be based on one of three options a stereogenic element can be introduced in the alkyne side chain, in the carbene carbon side chain or - most general and most attractive - in the heteroatom carbene side chain (Scheme 20). 

Semmelhack ME, Chlenov A (2004) (Arene)Cr(Co)3 Complexes Arene Lithiation/Reaction with Electrophiles. 7 21-42... 

Arenes, on complexation with Cr, Fe, Mn, and so forth, acquire strongly electrophilic character such complexes in reactions with nucleophiles behave as electrophilic nitroarenes.71 Synthesis of aromatic nitriles via the temporary complexation of nitroarenes to the cationic cyclopentadienyliron moiety, cyanide addition, and oxidative demetalation with DDQ has been reported (Eq. 9.43).72... 

Scheme 14.16 Stereocontrolled 1,4-hydrogenation of a carba-cyclin analogue using [Cr(CO)3(arene)] (45) complexes.

Correlation between o parameters and k (CO) for substituted arene Cr(CO)3 complexes... 

Uemura M (2004) (Arene)Cr(Co)3 Complexes Cyclization, Cycloaddition and Cross Coupling Reactions. 7 129-156 Ujaque G, see Drudis-Sole G (2005) 12 79-107 Urrutigoity M, see Kalck P (2006) 18 97-123... 

Planar chiral arene Cr(CO)3 complexes have been shown to undergo highly diastereoselective cycloadditions and Kiindig has extended this protocol to the [3+2] cycloadditions of azomethine ylides (96). Enantiopure ortho- substituted p -benzaldehyde complex 337 underwent condensation with an ot-amino ester to afford imine 338 in the presence of EtaN. Subsequent treatment with methyl acrylate at ambient temperamre in the presence of LiBr and EtaN delivered cycloadduct 339, with excellent stereoinduction and high material yield. Photoinduced oxidative decomplexation in air furnished the final arylpyrrolidines (Scheme 3.114). 

TABLE I Reaction of Arenes with 4 g of Cr(CO)6 to Give the Corresponding Complexes (ij6-Arene)Cr(CO)3a... 

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