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Titanium cis ‐1,2‐Diaminocyclohexane Salalen Catalysts of Outstanding Activity and Enantioselectivity for the Asymmetric Epoxidation of Nonconjugated Terminal Olefins with Hydrogen Peroxide
Author(s) -
Lansing Markus,
Engler Hauke,
Leuther Tobias M.,
Neudörfl JörgM.,
Berkessel Albrecht
Publication year - 2016
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201601154
Subject(s) - catalysis , chemistry , hydrogen peroxide , aldehyde , organic chemistry , nitro , chemoselectivity , halide , medicinal chemistry , alkene , aqueous solution , alkyl
We report a new and readily accessible class of titanium salalen complexes derived from cis ‐1,2‐diaminocyclohexane ( cis ‐DACH) and fluorinated salicylic aldehyde derivatives. With aqueous hydrogen peroxide as the oxidant, these complexes catalyze the epoxidation of terminal, nonconjugated olefins in high yields with high enantioselectivities. We furthermore discovered that the addition of certain acidic or basic co‐catalysts significantly accelerated the epoxidation. For example, in the presence of 1 mol % Ti catalyst and 1 mol % pentafluorobenzoic acid, 1‐octene epoxidation (95 % ee ) was completed at room temperature within 8 h. The catalytic process was compatible with many functional groups (e.g., ethers, esters, halides, nitriles, and nitro groups), whereas free hydroxy groups appeared to slow down the reaction to some extent. Catalyst recycling was possible.