Erika Nakashima

Asymmetric Aldol Synthesis: Choice of Organocatalyst and Conditions

This is the first report of a successful asymmetric aldol reaction of acetone and 4-nitrobenzaldehyde catalyzed by only 0.01 mol % of proline tetrazole (5-pyrrolidin-2-yltetrazole). Amazingly, 3 mol % of water as an additive has significantly improved the efficiency of the aldol reaction in terms of yield and enantioselectivity, up to a 0.1-mol-scale production (up to 99 % isolated yield, 84 % ee).

Process Catalyst Mass Efficiency by Using Proline Tetrazole Column-Flow System

Generally, organocatalysts are not decomposed during chemical transformation, which is different from traditional metal catalysts. To improve catalytic processes efficiency, various studies have been applied to flow synthesis for organocatalysis. Furthermore, many immobilized organocatalysts have been used for heterogeneous flow synthesis, which requires huge amounts of immobilized catalyst and requires several steps to prepare. We took advantage of organocatalysts with low-polarity organic solvent and developed a flow system through a packed-bed column with simply proline tetrazole (5-(2-pyrrolidinyl)-1H-tetrazole) for heterogeneous organocatalytic synthesis. Under ambient temperature, this heterogeneous organocatalyst continuous flow-column system with ketones as a donor provides aldol, Mannich, and o-nitroso aldol reactions in up to quantitative yields with excellent enantio- and chemoselectivity values. Our heterogeneous-flow synthesis provides extremely low process catalyst mass efficiency and continuous production without changing the packed-bed catalyst column.