Development of solid catalysts for selective reactions and their application to continuous-flow reactions

The development of "selective" reaction catalysts has considerable research interest in synthesizing fine chemicals and bioactive compounds. We have developed four types of solid-state heterogeneous palladium catalysts immobilized on cellulose particles (CLP), monolithic cellulose (CLM), and monolithic silica particles (SM), 5% Pd/CLP, 5% Pd/CLM, 5% Pd/SM, and 0.25% Pd/ SM(sc)[sc: supercritical], for chemoselective hydrogenation under batch and continuous-flow reaction conditions. These four catalysts indicate novel chemoselectivity toward hydrogenations based on the structure of supports and immobilization methods, even using the same techniques or materials. 5% Pd/CLM, 5% Pd/SM, and 0.25% Pd/SM(sc)-packed catalyst cartridges for continuous-flow hydrogenation were also developed as efficiently utilizing the monolithic structure of the solid-state catalysts. The continuous-flow system using such catalysts could achieve high productivities of the hydrogenated products. Furthermore, the tertiary amine- functionalized basic anion exchange resin WA30, as a solid-state organocatalyst, catalyzed synthesis of site-selectively deuterium-labeled β -nitroalcohols have been developed under both batch and continuous-flow conditions. The WA30-catalyzed deuteration of nitromethane in deuterium oxide and the subsequent nitroaldol reaction proceeded to provide the bis-deuterium- labeled β -nitroalcohols in high yields and high deuterium contents. The WA30-packed catalyst cartridge can be applied in continuous synthesis for at least 72 h without degradation of the catalyst activity. © 2021 Society of Synthetic Organic Chemistry. All rights reserved.