Ni-Catalyzed
Carboxylation of C(sp<sup>2</sup>)–
and C(sp<sup>3</sup>)–O Bonds with CO<sub>2</sub>
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Abstract
In
recent years a significant progress has been made for the carboxylation
of aryl and benzyl halides with CO<sub>2</sub>, becoming convenient
alternatives to the use of stoichiometric amounts of well-defined
metal species. Still, however, most of these processes require the
use of pyrophoric and air-sensitive reagents and the current methods
are mostly restricted to organic halides. Therefore, the discovery
of a mild, operationally simple alternate carboxylation that occurs
with a wide substrate scope employing readily available coupling partners
will be highly desirable. Herein, we report a new protocol that deals
with the development of a synergistic activation of CO<sub>2</sub> and a rather challenging activation of inert C(sp<sup>2</sup>)–O
and C(sp<sup>3</sup>)–O bonds derived from simple and cheap
alcohols, a previously unrecognized opportunity in this field. This
unprecedented carboxylation event is characterized by its simplicity,
mild reaction conditions, remarkable selectivity pattern and an excellent
chemoselectivity profile using air-, moisture-insensitive and easy-to-handle
nickel precatalysts. Our results render our method a powerful alternative,
practicality and novelty aside, to commonly used organic halides as
counterparts in carboxylation protocols. Furthermore, this study shows,
for the first time, that traceless directing groups allow for the
reductive coupling of substrates without extended π-systems,
a typical requisite in many C–O bond-cleavage reactions. Taking
into consideration the limited knowledge in catalytic carboxylative
reductive events, and the prospective impact of providing a new tool
for accessing valuable carboxylic acids, we believe this work opens
up new vistas and allows new tactics in reductive coupling events