Carbon dioxide in organic synthesis

Carbon dioxide is an abundant, cheap, almost nontoxic, thermodynamically stable, inert electrophile. Exploitation of CO 2 as a chemical feedstock, although will almost certainly not reduce its atmospheric concentration significantly, aims to generate high-value products and more-efficient processes. In recent years efficient transition-metal complexes have been used to perform homogeneously catalyzed transformations of CO 2 . This paper presents an overview of available catalytic routes for the synthesis of carboxylic acids, lactones, urea and carbamates, linear and cyclic carbonates as well as polycarbonates. Reduction processes of CO 2 are shortly men - tioned as well. C arboxylic acids have been synthesized via : (i) carboxylation of organolithium, organomagnesium (Scheme 2 [35]), organoboron (Scheme 3 [40 -42]), organozinc (Scheme 4 [43, 44]) and organotin (Scheme 5 [45, 46]) compounds; (ii) oxidative cycloaddition of CO 2 to olefins and alkynes (Scheme 6 -10 [47 -50, 57]) catalyzed by Ni(0)-complexes; (iii) transition-metal catalyzed reductive hydrocarboxylation of unsaturated compounds (Scheme 11, 12 [64 -67]); (iv) carboxylation of C-H bond (Scheme 13 [69 -71]). Telomerization of dienes, for instance 1,3-butadiene, and CO 2 in the presence of Ni(II) and Pd(II) complexes leads to lactones and esters of carboxylic acids (Scheme 14, 15 [73 -79]). Nucleophilic ammonia, primary and secondary amines react with CO 2 to give, respectively, urea and carbamic acid esters - carbamates and isocyanates (Scheme 16 -18 [94, 95]), thus eliminating the use of phosgene in their synthesis. CO 2 reacts with alcohols, diols and epoxides in the presence of transition-metal complexes (Fig. 2) and the reaction products are: linear carbonates (Scheme 20, 21 [110 -118]), cyclic carbonates (Scheme 22 -24 [153 -170]) and polycarbonates (Scheme 25, 26, Fig. 3, Tab. 1 [179 -186]). Finally, hydrogenation of CO 2 , leading to the formation of CO, HCOOH, CH 3 OH, CH 4 , C 2 H 6 and C 2 H 4 (Scheme 27), as well as electrochemical and photochemical reductions in the pre - sence of homogeneous and heterogeneous catalysts have been shortly reviewed