Direct Carboxylation of C(sp3)-H and C(sp2)-H Bonds with CO2 by Transition-Metal-Catalyzed and Base-Mediated Reactions

Immacolata Tommasi

doi:10.3390/catal7120380

Abstract

This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach. The review is not intended to be comprehensive, but aims to analyze representative examples from the literature, including transition-metal catalyzed carboxylation of benzylic and allylic C(sp3)-H functionalities using CO2 which is at a “nascent stage”. Examples of light-driven carboxylation reactions of unactivated C(sp3)-H bonds are also considered. Concerning C(sp3)-H and C(sp2)-H deprotonation reactions mediated by bases with subsequent carboxylation of the carbon nucleophile, few examples of catalytic processes are reported in the literature. In spite of this, several examples of base-promoted reactions integrating “base recycling” or “base regeneration (through electrosynthesis)” steps have been reported. Representative examples of synthetically efficient, base-promoted processes are included in the review.

Highlights

Viable and efficient conversion of CO2 into chemicals and fuels is a challenging goal and, at the same time, a subject of scientific debate [1]
This review focuses on recent advances in the field of direct carboxylation reactions of C(sp3)-H and C(sp2)-H bonds using CO2 encompassing both transition-metal-catalysis and base-mediated approach
Concerning C(sp3)-H and C(sp2)-H deprotonation reactions mediated by bases with subsequent carboxylation of the carbon nucleophile, few examples of catalytic processes are reported in the literature

Summary

Introduction

Viable and efficient conversion of CO2 into chemicals and fuels is a challenging goal and, at the same time, a subject of scientific debate [1]. The LnCo(I)Me active species is proposed to form through LnCo(II) alkylation by AlMe3 to LnCo(II)Me2 and subsequent disproportionation of the latter to LnCo(III)Me3 and LnCo(I)Me. Very recently Mita and Sato have reported the catalytic carboxylation of allylic C(sp )‐H bond of terminal alkenes with CO2 in the presence of a Co(acac)2/Xantophos/AlMe3/CsF system [53] (Scheme 12). The reaction consists in selective proton abstraction from phenyl allyl ethers (20) by (iBu)3Al(TMP)Li (2 eq.) (28) to obtain an η1-allyl-anion coordinated to Al (21) that undergo subsequent transmetallation/carboxylation in the presence of the [(IMes)Cu(OtBu)] catalyst (29) to give methyl 3-butenoate derivatives (22) in high yield and high stereoselectivity. As reported in the introductory section, direct carboxylation of aromatic and/or heteroaromatic substArasterespworitthedCiOn 2thheasinrterocediuvcetdorpyasreticctuiolanr, datitreenctticoanrbinoxtyhleatliaosnt odfeacraodme.aEtixccaenllden/otrrheevtieerwosaroonmtahtiisc

Carboxylation of Alkenyl-C-H Bonds by Pd-Catalysis

Carboxylation of Aromatic and Heteroaromatic Compounds

Findings

C-H Carboxylation with CO2 via Heterogeneous Catalysis