Nickel-Catalyzed Reductive Carboxylation and Amidation of Organic Matter

In recent years, the development of metal-catalyzed reductive carboxylation of organic (pseudo)halides with carbon dioxide (CO₂) for preparing carboxylic acids has become a powerful alternative to the classical use of well-defined, and in most instances, air-sensitive organometallic species. However, the use of simple unprotected alcohols or unsaturated hydrocarbons in combination with CO₂ to obtain carboxylic acids via a C-C bond forming reaction have received much less attention. They represent an attractive alternative to traditional organic halides, since they are abundant and readily available. We describe in this doctoral thesis the site-selective carboxylation of unprotected allylic alcohols with CO₂, a methodology that is able to deliver unsaturated carboxylic acids with excellent control of the selectivity obtained. Moreover, a novel nickel-catalyzed site-selective dicarboxylation of 1,3-dienes (including bulk 1,3-butadiene, isoprene or piperylene feedstocks) is described, in which different substituted adipic acids have been prepared. With all the knowledge gathered by our group regarding the carboxylation with CO₂, we moved our attention to the use of isotopically enriched CO₂ to prepare isotopically labeled carboxylic acids by means of nickel catalysis in a simple 2-step sequence. Finally, we have also investigated the use of isocyanates, isoelectronic with CO₂, as amide synthons. Its combinations with secondary alkyl bromides allowed us the study of different ligands that promoted or suppressed b-hydride elimination from the alkyl-nickel intermediates, delivering a regiodivergent transformation to obtain the corresponding amide in the initial or in a remote position. Overall, the synthetic methods developed during this Doctoral Thesis have given access to a variety of carboxylic acids and amides via Ni-catalyzed reductive couplings, increasing the ways of using heteroallenes for chemical synthesis.

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