- Modular synthesis of functionalisable alkoxy-tethered N-heterocyclic carbene ligands and an active catalyst for buchwald-hartwig aminations
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Modular syntheses of functionalised, alkoxy-tethered 1,3-bis(2,4,6- trimethylphenyl)imidazolium (IMes*H+) and 1,3-bis(2,6- diisopropylphen-l)imidazolium (IPr*H+) derivatives 1,3-bis(4-alkyl- -2,4,6-trimethylphenyl)imidazolium (IXyOR*H+) and 1,3-bis(4-alkyl-oxy-2,6-diisopropylphenyl)imidazolium (IPrOR*H +) are reported. A reliable synthesis of the key starting material 4-amino-3,5-diisopropylphenol is also described. Etherification of hydroxydecorated ligand intermediates before formation of the imidazolium core and subsequent modification, or direct etherification of the versatile synthon IPrOH·HCl, allowed access to various linker types including triethoxysilyl, primary amino and norbornenyl, which are not accessible by other methods. An IPrOR-palladium(II) complex was prepared, and its catalytic activity was evaluated in challenging Buchwald- Hartwig aminations of aryl chlorides. This precatalyst displayed excellent activity and selectivity under mild reaction conditions, achieving in some cases a 10-fold improvement in TOF relative to the IPr-based version. An unexpected activity profile was observed wherein sterically demanding anilines were coupled more easily than those lacking orthosubstitution.
- Krinsky, Jamin L.,Martinez, Alberto,Godard, Cyril,Castillon, Sergio,Claver, Carmen
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p. 460 - 474
(2014/05/20)
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- Aprotic diazotization in the presence of cuprous cyanide
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In a procedure of extreme simplicity and rapidity a mixture of an aromatic primary amine, copper (I) cyanide and an alkyl nitrite in dimethyl sulphoxide yielded fair to moderate yields of the corresponding nitriles. Side processes observed were reduction (NH2&[H), nitration (NH2←NO2) and hydroxylation (NH2&[OH). In the case of polyhaloanilines halogen dance products could be detected.
- Giumanini, Angelo G.,Verardo, Giancarlo,Geatti, Paola,Strazzolini, Paolo
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p. 7137 - 7148
(2007/10/03)
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- The Rearrangement of Aromatic Compounds. Part 3. The Mechanism of Rearrangement of Nitrated Hydrocarbons in Trifluoromethanesulphonic Acid
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1,3-Dialkyl-2-nitrobenzenes (C6H3R2NO2; R = Me, Et, and Pri) rearrange in trifluoromethanesulphonic acid to the corresponding 4-nitro derivatives; with R = Et, this reaction is accompanied by dehydration to 7-ethyl-3-methylanthranil.The reaction rate increases markedly with the size of the alkyl group; with R = Me, the reaction was studied at 110 deg C but, with R = Pri, temperatures of 36-54 deg C were used.The studies with R = Me show the reaction to be first-order with the rate coefficients (k1) increasing rapidly with the acidity of the solution 1)/d(-H0)> = 1.45, decreasing with acidity to o.49.Double-labelling experiments with 1H and 15N show the reaction to be intramolecular. 1,2,4-Trimethyl-3-nitrobenzene also rearranges under these conditions to give mainly the 5-nitro isomer.The above results are discussed in terms of a direct 1,3-shift of the nitro group.
- Bullen, John V.,Ridd, John H.,Sabek, Omaima
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p. 1681 - 1685
(2007/10/02)
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