- Selective esterifications of alcohols and phenols through carbodiimide couplings
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Esterification of carboxylic acids capable of forming ketene intermediates upon treatment with carbodiimides permits the selective acylation of alcohols in the presence of phenols lacking strong electron-withdrawing groups. The selectivity of acylations involving highly acidic phenols could be reversed through the addition of catalytic amount of acid. Esterification of other carboxylic acids was found to proceed through the formation of symmetric anhydrides and provide the opposite chemoselectivity. In both cases the relative acylation rates of substituted phenols are consistent with a reaction mechanism involving an attack of phenolate anions on electrophilic intermediates such as ketenes and symmetric anhydrides, with the carbodiimides serving both as an activating reagent and as a basic catalyst.
- Shelkov, Rimma,Nahmany, Moshe,Melman, Artem
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p. 397 - 401
(2007/10/03)
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- Reductive elimination of aryl carboxylates from acyl(aryloxy)nickel(II) and -palladium(II) complexes
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Acyl(p-cyanophenoxy)nickel(II) and -palladium(II) complexes, M(COR)(OC6H4-p-CN)L2 (M = Ni, Pd; L2 = bpy, (PEt3)2), have been prepared by insertion reactions of CO into the metal-carbon bonds of the corresponding methylnickel(II) and -palladium(II) complexes. Addition of π-acids such as CO, maleic anhydride, and acrylonitrile selectively induces reductive elimination of p-cyanophenyl acetate from acylnickel(II) complexes, whereas thermolysis of the complexes mainly results in decarbonylation. In contrast, reductive elimination from the palladium analogue proceeds smoothly on thermolysis, and no apparent accelerating effect of added π-acids is observed. Kinetic studies of both reductive eliminations reveal that the former proceeds via an associative mechanism involving a five-coordinate intermediate, whereas the latter proceeds via two mechanisms, one being a dissociative pathway involving a three-coordinate species and the other being a direct reductive elimination from a four-coordinate species.
- Komiya, Sanshiro,Akai, Yasushi,Tanaka, Kohkichi,Yamamoto, Takakazu,Yamamoto, Akio
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p. 1130 - 1136
(2008/10/08)
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- 2'Hydroxy tetrazole-5-carboxanilides and anti-allergic use thereof
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New tetrazole derivatives of the general formula: STR1 [wherein R1 represents a halogen atom, a straight- or branched-chain alkyl, alkoxy, alkylthio, alkylsulphinyl, alkylsulphonyl or alkylsulphamoyl group, each such group containing from 1 to 6 carbon atoms, a dialkylsulphamoyl, dialkylamino, or dialkylcarbamoyl group (wherein the two alkyl groups may be the same or different and each contains from 1 to 4 carbon atoms), a straight- or branched-chain alkanoyl, alkoxycarbonyl, alkoxycarbonylamino, alkylcarbamoyl or alkanoylamino group containing from 2 to 6 carbon atoms, a cycloalkylcarbonyl group containing from 3 to 8 carbon atoms in the cycloalkyl moiety, or a hydroxy, formyl, nitro, trifluoromethyl, trifluoroacetyl, aryl, benzyloxycarbonylamino, amino, sulphamoyl, cyano, tetrazol-5-yl, carboxy, carbamoyl, benzyloxy, aralkanoyl or aroyl group, or a group of the formula: (wherein R2 represents a hydrogen atom or a straight- or branched-chain alkyl group containing from 1 to 5 carbon atoms, an aryl, aralkyl or trifluoromethyl group, or a cycloalkyl group containing from 3 to 8 carbon atoms, and R3 represents a hydrogen atom, or a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms optionally substituted by a phenyl group, or represents an aryl group optionally substituted by one or more substituents selected from halogen atoms and straight- or branched-chain alkyl and alkoxy groups containing from 1 to 6 carbon atoms and hydroxy, trifluoromethyl and nitro groups), and m represents zero or an integer 1, 2 or 3, the substituents R1 being the same or different when m represents 2 or 3] possess pharmacological properties, in particular properties of value in the treatment of allergic conditions.
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- Insertion of Carbon Monoxide into Nickel-Alkyl Bonds of Monoalkyl- and Dialkylnickel(II) Complexes, NiR(Y)L2 and NiR2L2. Preparation of Ni(COR)(Y)L2 from NiR(Y)L2 and Selective Formation of Ketone, Diketone, and Aldehyde from NiR2L2
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Reactions of monoalkylnickel(II) complexes, NiR(Y)L2 (R=CH3, C2H5; Y=Cl, suc(succinimido), pht(phthalimido), OC6H4-p-CN; L=1/2 bpy (2,2'-bipyridine), PEt3 (triethylphosphine)), with CO afford monoacylnickel(II) complexes, Ni(COR)(Y)L2, which are characterized by elemental analysis and spectroscopies (IR and NMR).Reactions of the acylnickel(II) complexes with alcohols and aniline give the corresponding esters and amides, respectively.Exposure of Ni(COR)(Y)L2 to dry air leads to oxidation of RCO to a RCOO ligand giving a complex formulated as NI(OCOR)(Y)L2.Reactions of dimethylnickel(II) complexes, Ni(CH3)2L2 (L=1/2 bpy, PEt3, 1/2dpe (1,2-bis(diphenylphosphino)ethane, 1/2 dpp (1,3-bis(diphenylphosphino)propane), with carbon monoxide afford acetone and/or 2,3-butanedione in medium to high yields, the acetone/2,3-butanedione ratio varying with the ligand L, reaction temperature, and additives such as maleic anhydride and triphenylphosphine.Generally the acetone/2,3-butanedione ratio decreases with increase in thermal stabilities of Ni(CH3)2L2.Ni(C2H5)2(bpy) and Ni(n-C3H7)2(bpy) give 3-pentanone and 4-heptanone, respectively, on treating them with CO, whereas Ni(C2H5)2(dpe) produces C2H5CHO and C2H4.
- Yamamoto, Takakazu,Kohara, Teiji,Yamamoto, Akio
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p. 2161 - 2168
(2007/10/02)
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