- Regioselective halogen-metal exchange reaction of 3-substituted 1,2-dibromo arenes: The synthesis of 2-substituted 5-bromobenzoic acids
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Regioselective halogen-metal exchange reactions using isopropylmagnesium chloride were carried out on 3-substituted 1,2-dibromo arenes. Eleven examples are given. Georg Thieme Verlag Stuttgart.
- Menzel, Karsten,Dimichele, Lisa,Mills, Paul,Frantz, Doug E.,Nelson, Todd D.,Kress, Michael H.
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p. 1948 - 1952
(2008/02/08)
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- Halogen-metal exchange of 3-substituted 1,2-dibromoarenes: The use of long-range JCH coupling constants to determine regiochemistry
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Regioselective halogen/metal exchange reactions were carried out on a series of 3-substituted-1,2-dibromoarenes. Product mixtures were quenched with CO2 to form the corresponding benzoic acid analogs to facilitate HPLC and NMR analysis. Substitution at the 3-position could readily be assigned on the basis of 2D HMBC long-range correlations, while assignment at the 2-position was not as straightforward. The use of three-bond JCH coupling constant measurements, extracted from 1-D 1H coupled 13C experiments, were necessary to render unequivocal regio assignments. Copyright
- DiMichele, Lisa,Menzel, Karsten,Mills, Paul,Frantz, Doug,Nelson, Todd
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p. 1041 - 1043
(2008/02/05)
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- Ortho-metalation of unprotected 3-bromo and 3-chlorobenzoic acids with hindered lithium dialkylamides
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Upon treatment of 3-chloro/bromobenzoic acids with hindered lithium dialkylamides (LDA or LTMP) at -50 °C, lithium 3-chloro/bromo-2-lithiobenzoates are generated. These dianions can be trapped as such to afford after electrophilic quenching a variety of s
- Gohier, Frederic,Mortier, Jacques
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p. 2030 - 2033
(2007/10/03)
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- The acidifying effects of chlorine and bromine: Little difference
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Lithium diisopropylamide deprotonates ortho- and para-bromochlorobenzene randomly at the two halogen adjacent positions. Obviously for steric reasons, the bulkier base lithium 2,2,6,6-tetramethylpiperidide favors the attack in the vicinity of the chlorine rather than the bromine atom to the extent of 2:1. At -75°C, both 2-bromo-3-chlorophenyllithium and 3-bromo-2-chlorophenyllithium isomerize to give 2-bromo-6-chlorophenyllithium. The latter species can be directly generated from 1-bromo-3-chlorobenzene.
- Mongin, Florence,Schlosser, Manfred
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p. 1559 - 1562
(2007/10/03)
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- Lithiations directed by carboxylic acid, fluorine and chlorine: The regioselective synthesis of polysubstituted benzoic acids and acetophenones
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Lithiation/electrophilic quenching of ortho-lithiated benzoates allows the totally regiocontrolled synthesis of a wide range of 2,3-, 2,3,4-, and 2,3,4,5-polysubstituted benzoic acids and related acetophenones. Elsevier,.
- Moyroud, Joel,Guesnet, Jean-Luc,Bennetau, Bernard,Mortier, Jacques
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p. 133 - 141
(2007/10/03)
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- Directed lithiation of unprotected benzoic acids
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Benzoic acid gives the ortho-lithiated species 1 under standard conditions (s-BuLi-TMEDA-THF, -90 deg C).Reaction of 1 at -78 deg C with either methyl iodide, dimethyl disulfide, hexachloroethane, or 1,2-dibromotetrachloroethane gives the ortho-substituted product.Intramolecular competition between the carboxylic acid and methoxy, chloro, fluoro, or diethylamido functions in ortho- and -para-substituted benzoic acids establishes the carboxylic acid group to be of intermediate capacity in directing metallation.Complimentarity of directing effects is observed with the chloro and fluoro groups in the meta-substituted benzoic acid but not with the methoxy and trifluoromethyl groups.Electrophile introduction into meta- and para-lithiated benzoates occurs with equal efficacy and comparable scope.The 2,4-dihalogenobenzoic acids undergo hydrogen/metal exchange at the position flanked by both halogen substituents. 2,2-Difluoro-1,3-benzodioxole-4-carboxylic acid undergoes lithiation adjacent to the oxygen atom.By use of such methods, routes to benzoic acids contiguously tri- and tetra-substituted with a variety of functionalities have been developed.
- Bennetau, Bernard,Mortier, Jacques,Moyroud, Joel,Guesnet, Jean-Luc
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p. 1265 - 1272
(2007/10/02)
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- Regiospecific Synthesis of Mixed 2,3-Dihalobenzoic Acids and Related Acetophenones via Ortho-Metalation Reactions
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Concise general routes to mixed 2,3-dihalobenzoic acids and related acetophenones-based on directed ortho-metalation and ipso-desilylation reactions are described.
- Moyroud, Joel,Guesnet, Jean-Luc,Bennetau, Bernard,Mortier, Jacques
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p. 881 - 884
(2007/10/02)
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