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2.6.1.2 Carboxylation of C—H and N—H Bonds Catalyzed by Copper(I) Hydroxide Complexes

DOI: 10.1055/sos-SD-224-00164

Nelson, D. J.Science of Synthesis: N-Heterocyclic Carbenes in Catalytic Organic Synthesis, (20162283.

Carboxylation reactions of the type described in Section 2.6.1.1 can also be catalyzed by the corresponding copper(I) hydroxide or tert-butoxide complexes [the latter is generated in situ from the copper(I) chloride],[‌4‌,‌5‌] and occur via a similar mechanism. The pKa range to which this methodology is applicable is slightly different [substrates with pKa (DMSO) <27.7 for Cu(OH)(IPr); some substrates with higher pKa react, albeit sluggishly, with Cu(Ot-Bu)(IPr) as the catalyst]. Hou and co-workers have demonstrated the C—H carboxylation of a number of heteroaromatic substrates, quenching the carboxylate with 1-iodohexane to yield the ester, with the scope effectively limited to benzoxazoles;[‌5‌] Cazin and Nolan et al. explored some (hetero)aromatic substrates as well as carboxylation of the N—H bonds of some hetarenes 6, quenching the reactions either with hydrogen chloride to deliver the carboxylic acid or iodomethane to prepare the methyl esters 7.[‌4‌] Some examples of these N—H carboxylation reactions are shown in Table 1; unfortunately neither aniline nor 2,2,6,6-tetramethylpiperidine can be carboxylated in this way.

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88 [‌8‌]
88 [‌8‌]
88 [‌8‌]
88 [‌8‌]

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References


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