Multielectron Reduction of Esters by a Diazabenzacenaphthenium Photoredox Catalyst.

A novel diazabenzacenaphthenium photocatalyst, N-BAP, with high photoredox abilities and visible-light absorption was designed and prepared in one step. Under visible-light irradiation, N-BAP promoted the four-electron reduction of esters in the presence of ammonium oxalate as a "traceless reductant" to generate carbinol anion intermediates that underwent protonation with water to give the corresponding alcohols. The resulting carbinol anions also exhibited nucleophilic reactivity under the photocatalytic conditions to undergo a 1,2-addition to a second carbonyl compound, affording unsymmetric 1,2-diols.

Asymmetric Flow Reactions Catalyzed by Immobilized Diphenylprolinol Alkyl Ether: Michael Reaction and Domino Reactions.

Flow reactions using an immobilized diphenylprolinol alkyl ether catalyst 2 were investigated in three reactions of α,ß-unsaturated aldehydes and nitroalkanes such as nitromethane 3, nitroethanol 10, and nitroalkane 11, bearing two carbonyl groups. Whereas reactions using the corresponding monomer catalyst diphenylprolinol silyl ether 1 were slow, fast reactions were found with the immobilized polymer catalyst 2 in a batch system, and the latter was then applied to a flow system. In the Michael reaction of nitromethane 3, the polymer catalyst showed high reactivity in the initial 30 h and then decreased gradually. Good overall yield (72%) and turnover number (TON, 495) were obtained for a 60 h flow reaction, and the enantioselectivity of the product was excellent throughout. The TONs of domino reactions of nitroethanol 10 and nitroalkane 11, with two carbonyl groups, were 48 and 81, respectively.