1595-04-6

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Treatment of substituted aryl chlorides with functionalized organozinc iodides in the presence of catalytic amounts of a soluble Ni(0) source lead to efficient displacement reactions.

The Catellani reaction has received substantial attention because it enables rapid multiple derivatization on aromatics. While using alkyl electrophiles to achieve ortho-alkylation was one of the earliest applications of the Catellani reaction, ipso-alkyl

(Chemical Equation Presented) Overcoming the ortho/para rule? The regioselectivity of Diels-Alder reactions with neutral electron demand between 1,3-dienes with alkynes can be controlled by simple cobalt diimine complexes so that the meta-substituted cycloadducts are generated in good yields and excellent regioselectivity (see scheme; DDQ=2,3-dichloro-5,6-dicyano-1,4- benzoquinone).

Reductive alkylation of benzonitrile, ortho-, meta-, para-tolunitriles, and 1-naphthonitrile by sequential action of alkali metal and alkyl bromide in liquid ammonia results in corresponding alkylarenes and 1-alkyl-1- cyanocyclohexa-2,5-dienes. The experimental conditions for target synthesis of the specified products are found. A method of synthesis of 1-(ω- bromoalkyl)-1-cyanocyclohexa-2,5-dienes based on the interaction of two-electronic reduction products of aromatic nitriles with α,ω- dibromoalkanes Br(CH2)nBr (n = 3-5) is developed.

The interaction of terephthalonitrile (1) dianion (12-) with benzonitrile (2) or m-tolunitrile (3) provides 4,4′-dicyanobiphenyl (4) or 4,4′-dicyano-2-methylbiphenyl (5), respectively. This result shows that dianion 12- serves as a reagent for p-cyanophenylation of aromatic nitriles. Based on experimental data, such as the chemical trapping of the 4,4′-dicyanobiphenyl precursor 4-cyano-1-(p-cyanophenyl)cyclohexa-2,5-dienyl anion (7) and the failure to obtain biphenyl 4 through the interaction of independently generated radical anions (RAs) 1- and 2-, as well as on the results of quantum-chemical calculations, a mechanism is suggested that includes a charge-transfer complex (CTC) between 12- and the aromatic nitrile as the key intermediate. The formation of this CTC is followed either by an intracomplex electron transfer (ET) and recombination of terephthalonitrile and aromatic nitrile RAs within an unequilibrated RA pair, or by synchronous ET and bonding of the ipso-carbon atom of terephthalonitrile with the p-carbon atom of the aromatic nitrile. The synthetic significance of p-cyanophenylation of arenecarbonitriles by dianion 12- is illustrated by the high yield of biphenyl product 4 (approx. 90%) as well as by the possibility of a one-pot synthesis of 4-butyl-4′-cyanobiphenyl and 4-butyl-4′-cyano-2-methylbiphenyl by successive treatment of dianion 12- with nitrile 2 or 3 and butyl bromide. Wiley-VCH Verlag GmbH & Co, KGaA, 69451 Weinheim, Germany, 2005.

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Protocols for aromatic aminations and Kumada couplings catalyzed by 'heterogeneous' nickel-on-charcoal (Ni/C) have been revised, making them simpler and more time efficient. For both types of reactions, reduction of the catalyst precursor Ni(II)/C using n-BuLi prior to addition of a substrate can be avoided. Instead, in amination reactions, the amine in combination with lithium tert-butoxide was found to convert Ni(II)/C to active Ni(0). For Kumada couplings, direct reduction of Ni(II)/C by the Grignard reagent is easily achieved. Reactions run in the presence of triarylphosphine ligands of varying substitution patterns and with differing electronic properties provided insight into the mechanism of these nickel-catalyzed transformations. Ligandless Kumada couplings were facile with aryl Grignards, which may be a consequence of π-complexation of nickel by the aryl group in the reagent. Larger scale reactions of both types of couplings have been successfully performed, suggesting that Ni/C-based processes can be scaled-up as needed.

Results from aromatic aminations and Kumada couplings, together with spectroscopic analyses (TEM, EDX, ICP-AES, React-IR), reveal that catalysis using nickel-on-charcoal (Ni/C) is most likely of a homogeneous rather than heterogeneous nature. In the course of a reaction with Ni/C, nickel bleed from the support was calculated to be as high as 78%. However, the existence of an equilibrium for this homogeneous species between nickel located inside vs outside the pore system of charcoal strongly favors the former, thus leaving only traces of metal detectable in solution. This accounts for virtually complete recovery of nickel on the charcoal following filtration of a reaction mixture and allows for recycling of the catalyst. TEM and EDX data were used to explain different reactivity profiles of Ni/C, which depended upon the method of reduction used to convert Ni(II)/C to Ni(0) as well as the level of nickel loading on the support.

Arylzincates bearing a leaving group at the ortho, meta, and para positions were generated by iodine/zinc exchange reaction of the corresponding iodoaryl sulfonates with Bu3ZnLi, and their reactivity was investigated via product analysis after hydrolysis and treatment with iodine. Zincates derived from o-iodophenyl triflates and tosylate underwent homologation reaction to give o-butylphenylzinc species. o-Benzyne as an intermediate of the reaction was demonstrated by the lack of regioselectivity for trisubstituted zincates. Zincates derived from m-iodophenyl triflates also underwent homologation leading to m-butylphenylzinc species. Similar product ratios observed in the reactions of regioisomeric trisubstituted iodophenyl triflates as well as the formation of radical reaction byproducts suggested the involvement of m-benzyne intermediate. p-(Trifluoromethane-sulfonyloxy)phenylzincate was thermally stable at room temperature; generation of p-benzyne was not observed.