Titanium-Catalyzed Asymmetric Epoxidation of Olefins with Aqueous Hydrogen Peroxide: Remarkable Effect of Phosphate Buffer on Epoxide Yield

Abstract

The practicality of Ti(salan)-catalyzed asymmetric ­epoxidation was significantly improved by the addition of phosphate buffer (pH 7.4-8.0). Various olefins were transformed on a multigram scale into the corresponding epoxides with nearly ­complete product selectivity as well as high to excellent enantio­selectivity in the presence of 1 mol% of the catalyst and the buffer.

Key words

asymmetric catalysis - epoxidation - titanium - hydrogen peroxide - green chemistry

References and Notes

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7

The main byproducts are hydroperoxyalcohols and diols.

8

A phospate buffer of pH 7.4-8.0 can be used for the purpose of suppressing the decomposition of epoxides.

9

Other buffers such as acetate, citrate, and borate buffers were also effective.

11

Unfortunately, reactions of aliphatic olefins were low productive in view of both yield and enantioselectivity, even under the optimized conditions.

12

In a large-scale synthesis, the addition of an excess amount of ligand was not required, while the excess ligand was added in a small scale in order to obtain reproducibility.