Ni-Catalyzed Carboxylation of C(sp²)– and C(sp³)–O Bonds with CO₂

Abstract

ABSTRACT:In recent years a significant progress has been made for the carboxylation of aryl and benzyl halides with CO 2 , becoming covenient 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, hence improving the flexibility in catalytic design while increasing our ever-growing synthetic arsenal. Herein, we report a new protocol that deals with the development of a synergistic activation of CO 2 and a rather challenging activation of inert C(sp 2 )−O and C(sp 3 )−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 without the use of any sensitive metal species. 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, inert C−O bond-cleavage 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.

Using carbon dioxide as a building block in organic synthesis

“…5b). Very recently, the same group reported a novel Ni-catalysed carboxylation of aryl esters with less-activated C-O bonds (Table 1, entry 18) 72 . This new protocol deals with the development of a synergistic activation of CO 2 and a rather challenging activation of inert C(sp 2 ) À O and C(sp 3 ) À O bonds derived from simple and cheap alcohols.…”

Nickel-Catalyzed Reductive Couplings

“…Accordingly, the recent elegant development on CO 2 fixation with C(sp 2 )-electrophiles [e.g., C(sp 2 )-O and benzyl C(sp 3 )-O bond activation] and alkynes is not discussed [96,97].…”

Nickel‐Catalyzed Reductive Benzylation of Aldehydes with Benzyl Halides and Pseudohalides

“…Also, on change of Zn with Mn no improvement in the reaction yield was observed, which shows that Zn is more efficient than Mn for this process (Table 1, entry 13). [22] Attempts to improve the yield by changing the solvent to NMP, acetonitrile and toluene were found to be fruitless (Table 1, entries [14][15][16]. Also, efforts to increase the yield by conducting the reaction at higher temperatures resulted in a decrease in the yield of the reaction ( (Table 1) are the optimal to offer the highest yield of the product in our designed protocol.…”

“…[27] The ultimate action of IV with Zn would regenerate the active Ni(0)·L 2 species and gives zinc alkoxy complex V. The complex V then undergoes hydrolysis with water to yield the target product. [16,22] …”