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Two new catalysts for continuous-flow synthesis

By Tetsuo Satoh |

Shu Kobayashi and colleagues at the University of Tokyo (Japan; www.chem.s.u-tokyo.ac.jp) reported on two new catalysts for synthesizing fine chemicals using their continuous-flow reactor system.

The first technology is a novel methodology using CsF.Al2O3 as a highly efficient, environmentally benign, and reusable solid-base catalyst to synthesize glutamic acid derivatives by stereoselective 1,4-addition of glycine derivatives to α,β-unsaturated esters. CsF.Al2O3 (with 40 wt.% CsF and thermal treatment at 200°C under vacuum) showed not only great selectivity toward 1,4-addition reactions (94% after 38 h) by suppressing the undesired formation of pyrrolidine derivations by [3+2] cycloadditions (with 1,4:[3+2] = 99:1), but also offered high yields for the 1,4-adduct with excellent anti diastereoselectivities (with anti:syn better than 99:1). Continuous-flow synthesis (for more than 50 days) of 3-methyl glutamic acid derivative was successfully demonstrated by using this solid-base catalysis. They are expecting that the developed procedure will be applied for the various continuous flow fine synthesis of stereoselective catalytic reactions.

The second technology is the hydrogenation of arenes, an important reaction not only for hydrogen storage and transport but also for the synthesis of functional molecules, such as pharmaceuticals and biologically active compounds. The researchers developed heterogeneous Rh–Pt bimetallic nanoparticle catalysts for the hydrogenation of arenes with inexpensive polysilane as support. The catalysts could be used in both batch and continuous-flow systems with high performance under mild conditions and showed wide substrate generality. In the continuous-flow system, the product could be obtained by simply passing the substrate and 1 atm H2 through a column packed with the catalyst. Remarkably, much higher catalytic performance was observed in the flow system than in the batch system, and extremely strong durability under continuous-flow conditions was demonstrated after a continuous run of more than 50 days. The turnover number was found to be more than 3.4 × 105.

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