Arenes ring substitution

Substituting deuterium for hydrogen gas in the reduction of BT to DHBT with the catalyst precursor [Rh(NCMe)3(Cp )](BF4)2 has shown that the stereoselective ds-deuteration of the double bond is kinetically controlled by the tj2-C,C coordination of BT. The incorporation of deuterium in the 2- and 3-positions of unreacted substrate and in the 7-position of DHBT has been interpreted in terms of reversible double-bond reduction and arene-ring activation, respectively (Scheme 16.14) [55]. 

The intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

Ring Substitution Reactions of Metal-Cyclopentadienyls and Metal-Arenes... 

This chapter covers reactions in which coordination of a transition metal to the ir-system of an arene ring activates the ring toward addition of nucleophiles, to give V-cyclohexadienyl-metal complexes (1 Scheme 1). If an electronegative atom is present in the ipso position, elimination of that atom (X in 1) leads to nucleophilic aromatic substitution (path a). Reaction of the intermediate with an electrophile (E+) can give disubstituted 1,3-cyclohexadiene derivatives (path b). If a hydrogen occupies the ipso posi-... 

A study of the selectivity of lariat aza[15] crown-5 (3.133) and BiBLE (bi-brachial lariat ether) diaza[18] crown-6 derived ligands (3.134) containing variously substituted arene rings showed that the Ag+ complex stability decreased as a function of the electron-withdrawing ability of the substituents, R, as measured by the substituents Taft o° inductive constant (a parameter measuring the electron-withdrawing... 

Adcock, W. and Abeywickrema, A.N., Concerning the origin of substituent-induced fluorine-19 chemical shifts in aliphatic fluorides carbon-13 and fluorine-19 nuclear magnetic resonance study of l-fluoro-4-phenylbicyclo[2,2,2]octanes substituted in the arene ring, J. Org. Chem., 47, 2945, 1982. 

The enantiomers +8 and -8 were generated by removal of the planar chirality due to the unsymmetrically substituted arene ring in the separated diastereoisomers (7a and 7b). By treatment with LiAlH4-AlCl3, the ester group was reduced to a methyl group, leaving the asymmetric Cr atom the only element of chirality in the complexes +8 and -8,... 

Trityl resins are particularly suitable for immobilization of nucleophilic substrates such as acids, alcohols, thiols, and amines. They are quite acid-sensitive and are cleavable even with acetic acid this is useful when acid-labile protecting groups are used. The stability of trityl resin can be tailored by use of substituted arene rings, as shown by chlorotrityl resin, which furnishes a more stable linker than the trityl resin itself. Steric hindrance also prohibits formation of diketopiperazines during the synthesis of peptides. Orthogonality toward allyl-based protective groups was demonstrated in the reverse solid-phase peptide synthesis of oligopeptides [30] (Scheme 6.1.4). 

The scope and value of the benzannulation reaction is further increased by the substitution pattern of the arene ring, which can be modified by the incorporation of allcynes bearing additional functional groups such as silyl, stannyl, or boryl substituents. These functional groups have been used in various palladium-catalyzed (cross)-coupling reactions [63, 64]. Further structural elaboration may be based on benzannulation followed by nucleophilic aromatic addition [63b]. 

The chemical or electrochemical reduction of [(arene)Mn(CO)3]+ (23+) can lead to bimolecular coupling through the arene rings, CO loss followed by dimerization, or arene ring slippage.134 Which mode of decomposition is followed depends on many factors, especially the nature of the arene. In the presence of P(OBu)3, these decomposition pathways are short circuited in favor of ETC substitution to give [(arene)Mn(CO)2P(OBu)3]+. For example, Fig. 6 shows that application of a reducing current for a... 

Organomagnesium compounds add to unsubstituted arenes only under forcing or Barbier conditions [1], On the other hand, aromatic rings substituted by electron-withdrawing groups are surprisingly susceptible to attack by organomagnesium compounds. The early work on reactions of hindered aryl ketones [2] has been little further developed [3], despite some reports which should surely be followed up, e.g. [4],... 

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