Facile Synthesis of Useful Carboxylic Acids by Electrochemical Carboxylation Masao Tokuda, Daijiro Furuya, Hirokazu Komatsu

Facile Synthesis of Useful Carboxylic Acids by Electrochemical Carboxylation

Masao Tokuda, Daijiro Furuya, Hirokazu Komatsu, Hirotaka Kanaya, Nobuhito Kurono, and Pt Zn Hisanori Senboku CO2 Division of Molecular Chemistry, Graduate School of Engineering, Hokkaido University, CO2H CO2H CO2H CO H Sapporo 060-8628, Japan 2 + +

Electrochemical fixation of carbon dioxide is a useful CO2H CO2H and attractive method for efficient synthesis of various 1 2 3 carboxylic acids. We previously reported that electrochemical carboxylation of allylic and propargylic halides, in CH3CN 89% 11% 0% 1 vinyl bromides, vinyl triflates, and phenyl-substituted in scCO2 53% 29% 18% alkenes proceeded efficiently to give the corresponding carboxylic acids in high yields when a magnesium metal Scheme 1 was used as a sacrificial anode.2 In this paper, we report facile synthesis of arenedicarboxylic acids and cyclic a- alkoxyl- or cyclic a-amino-a,b-unsaturated carboxylic acids by electrochemical carboxylation of polyaromatic CO2H HO C CO H compounds and lactone or lactam enol triflates. 2 2 Synthesis of Arenedicarboxylic Acids Electrochemical carboxylation of naphthalene in CO H acetonitrile containing 0.1M Et4NClO4 with a Pt cathode 2 and a Zn anode under an atmospheric pressure of carbon 4 5 dioxide gave two dicarboxylic acids 1 and 2 in 89% and in CH3CN 32% in CH3CN 100% 11% yields, respectively. When this electrolysis was in scCO 87% o 2 in scCO2 93% carried out in supercritical carbon dioxide (scCO2; 40 C, 7.5 MPa), acids 1, 2, and 3 were obtained in 53, 29, and Scheme 2 18% yields (Scheme 1). On the other hand, dicarboxylic acids 4 and 5 were obtained in high yields as a single product by similar electrochemical carboxylation of anthracene and phenanthrene, respectively (Scheme 2). Electrolysis of anthracene under supercritical conditions of carbon dioxide (scCO2) gave 4 in 87% yield, although O O O OTf the similar electrolysis in acetonitrile solution in the Pt Mg O CO2H presence of atmospheric CO gave a lower yield of 4 due 2 CO , DMF to low solubility of anthracene in acetonitrile. Other n n 2 n NiBr2•bpy results will also be reported. 6 7 3 Synthesis of Captodative Cycloalkenes Scheme 3 Lactone or lactam enol triflates were readily prepared from the corresponding lactone or lactam. Electro- chemical carboxylation of lactone enol triflates (6) in DMF containing 20 mol% of NiBr2gbpy with a Pt cathode and Mg anode under an atmospheric pressure of CO gave 2 O CO2H O CO2H O CO2H cyclic -alkoxyl- -unsaturated acids (7), captodative a a,b Ph cycloalkene, in good yields (Scheme 3). These alkenes are useful as synthetic intermediates. Various cyclic a- 8 (65%) 9 (63%) 10 (58%) alkoxyl-a,b-unsaturated acids 8-15 and cyclic a-amino- a,b-unsaturated acid 16 were obtained in the yields CO H CO H shown in Scheme 4. In the case of 15, electrolysis in the O 2 O 2 Ph O CO2H absence of Ni catalyst gave a higher yield (82%) of the product. 11 (74%) 12 (79%) 13 (75%) REFERENCES 1) (a) Kamekawa, H.; Senboku, H.; Tokuda, M. Boc O CO H N CO H Tetrahedron Lett. 1998, 39, 1591. (b) Senboku, H.; 2 O 2

Fujimura, Y.; Kamekawa, H.; Tokuda, M. Electro- CO2H chimica Acta 2000, 45, 2995. (c) Senboku, H.; Kanaya, H.; Fujimura, Y.; Tokuda, M. J. Electroanal. Chem. 14 (71%) 15 (55%; 82%*) 16 (53%) 2001, 507, 82. * Yield in the absence 2) Senboku, H.; Komatsu, H.; Fujimura, Y.; Tokuda, M. of Ni catalyst Synlett. 2001, 418 and references cited therein. 3) Senboku, H.; Kanaya, H.; Tokuda, M. Synlett.2002, Scheme 4 140.