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ortho-Metalation of Unprotected 3-Bromo and 3-Chlorobenzoic Acids with Hindered Lithium Dialkylamides

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journal contribution
posted on 11.02.2003, 00:00 by Frédéric Gohier, Jacques Mortier
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 simple 2-substituted-3-chloro/bromobenzoic acids. The 3-bromo-2-lithiobenzoate is less stable than the corresponding 3-chloro derivative and partly eliminates lithium bromide, thus setting free lithium 2,3- and 3,4-dehydrobenzoates that can be intercepted in situ with the hindered base.