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Self‐Supported Heterogeneous Titanium Catalysts for Enantioselective Carbonyl–Ene and Sulfoxidation Reactions
Author(s) -
Wang Xisheng,
Wang Xingwang,
Guo Hongchao,
Wang Zheng,
Ding Kuiling
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500239
Subject(s) - catalysis , ene reaction , enantioselective synthesis , titanium , chemistry , supramolecular chemistry , heterogeneous catalysis , combinatorial chemistry , organic chemistry , homogeneous , molecule , physics , thermodynamics
Abstract A new strategy for the heterogenization of chiral titanium complexes was developed by the in situ assembly of bridged multitopic BINOL ligands with [Ti(O i Pr) 4 ] without using a support. The assembled heterogeneous catalysts (self‐supported) showed excellent enantioselectivity in both the carbonyl–ene reaction of α‐methylstyrene with ethyl glyoxylate (up to 98 % ee ) and the oxidation of sulfides (up to >99 % ee ). The catalytic performance of these heterogeneous catalytic systems was comparable or even superior to that attained with their homogeneous counterparts. The spacers between the two BINOL units of the ligands in the assembled catalysts had significant impact on the enantioselectivity of the carbonyl–ene reaction. This demonstrates the importance of the supramolecular structures of the assemblies on their catalytic behavior. In the catalysis of sulfoxidation, the self‐supported heterogeneous titanium catalysts were highly stable and could be readily recycled and reused for over one month (at least eight cycles) without significant loss of activity and enantioselectivity (up to >99.9 % ee ). The features of these self‐supported catalysts, such as facile preparation, robust chiral structure of solid‐state catalysts, high density of the catalytically active units in the solids, as well as easy recovery and simple recycling, are particularly important in developing methods for the synthesis of optically active compounds in industrial processes.