Highly enantioselective homogeneous catalysis under continuous-flow conditions was established for the cobalt-catalyzed borohydride reduction of tetralone derivatives. A microreactor allowed higher reaction temperature with the residence time of 12 min than the corresponding batch system to maintain enantioselectivity as well as reactivity. The present system was directly applied to gram-scale synthesis to afford the reduced product with 92% ee.

The reductive carboxylation of α,β-unsaturated carbonyl compounds with carbon dioxide was studied. After the screening of various transition-metal complex catalysts and reducing agents, it was found that the combination of bis(acetylacetonato)cobalt(II) and diethylzinc could effectively afford the corresponding α-carboxylate in high yield from α,β-unsaturated nitriles. The product was obtained after esterification by trimethylsilyldiazomethane. The highly selective carboxylation was observed at the α-position in the present study.

The gaseous carbon dioxide incorporation reaction with α,β-unsaturated compounds was examined in the presence of a catalytic amount of bis(acetylacetonato)cobalt(II) and using diethylzinc as a reductant. After screening with various electron-withdrawing groups, both α,β-unsaturated nitriles and carboxamides were found to efficiently capture carbon dioxide to provide the corresponding carboxylates or malonates in good to excellent yields under mild conditions.

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