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Cyclic carbonates are obtained in good yields from terminal epoxides and carbon dioxide in an electrochemical nickel-catalysed reaction.

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The electrochemical, nickel-catalyzed carbon dioxide incorporation into 2-haloaryl epoxides led chemoselectively to different carboxylated products according to the nature of the substrate and to the catalytic system. Whereas terminal epoxide derivatives led to cyclic carbonates in good yields, disubstituted epoxides reacted through a first carbon-halogen bond carboxylation followed by epoxide ring opening. Five-membered ring benzolactones were selectively formed with cyclam as the ligand, whereas 6-membered ring isocoumarine derivatives were obtained using 2,2'-bipyridine.The synthesis of benzolactone structures such as coumarines or isocoumarines has attracted much attention due to their use as antitumoral, antifungal and antibacterial agents. 1 We describe here a new method of synthesis of isocoumarine and other benzolactone derivatives, based on the use of an electrochemical carboxylation of epoxide-containing aromatic halides. The synthesis of isocoumarine structures generally involves the cyclization of functionalyzed benzoic acid derivatives. 2,3 Oxidation reactions of indanones have also been described. 4,5 The electrochemical reactivity of terminal epoxides with carbon dioxide for the synthesis of cyclic carbonates has been examined. 6 The reaction was catalyzed by Ni(cyclam)Br 2 (cyclam = 1,4,8,11-tetraazacyclotetradecane), but could also be effected in good yields with Ni(bipy) 3 2+ , 2BF 4 -as the catalyst (bipy = 2,2'-bipyridine). 7 We now describe that different chemoselectivities could be observed in the related electrochemical carboxylation of difunctional aromatic compounds 1-4, bearing epoxide and halogen as the functional groups. 8The electrocarboxylation of substrates 1 and 2 in DMF catalyzed by Ni(cyclam)Br 2 in a single-compartment cell led to the selective incorporation of CO 2 into the oxirane ring to form the corresponding cyclic carbonates in quantitative yields 9 (Scheme 1). The best conditions for this reaction were found to be the use of a magnesium anode, with CO 2 bubbling into the solution at atmospheric pressure and KBr as the supporting electrolyte.The reaction proceeds through the Mg 2+ and Br -induced oxirane ring opening and the parallel CO 2 activation by coordination to electrogenerated Ni I (cyclam)Br complex. The process is followed by the addition of activated CO 2 to the bromoalcoholate and ring closure to the cyclic carbonate with bromide elimination 7 . Scheme 1Two products were isolated; the 2-bromo (or 2-chloro)phenyl carbonate and the corresponding dehalogenated styrene carbonate. The dehalogenation was more important with X = Br. The carboxylation of 1 and 2 catalyzed by Ni(bipy) 3 2+ 2BF 4 -led to very similar results. The presence of KBr as supporting electrolyte (as compared to the use of Bu 4 N + BF 4 -), was an important factor to obtain good conversions and yields of cyclic carbonate both with Nicyclam and Ni-bipy catalytic systems. Thus, yields of cyclic carbonate went from 80 to 7% by changing from KBr to Bu 4 N + BF 4 -in the Ni(bipy) 3 2+ 2BF 4 --catalyze...