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Chiral C 2 ‐Boron‐Bis(oxazolines) in Asymmetric Catalysis – A Theoretical Study of the Catalyzed Enantioselective Reduction of Ketones Promoted by Catecholborane
Author(s) -
Bandini Marco,
Bottoni Andrea,
Cozzi Pier Giorgio,
Miscione Gian Pietro,
Monari Magda,
Pierciaccante Rossana,
UmaniRonchi Achille
Publication year - 2006
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200600133
Subject(s) - chemistry , enantioselective synthesis , electrophile , boron , catalysis , hydride , medicinal chemistry , ketone , organic chemistry , stereochemistry , combinatorial chemistry , hydrogen
C 2 ‐Symmetrical boron complexes, prepared by the reactions of 2,2′‐methylenebis(oxazolines) (BOXs) with catecholborane (CATBH), can be used as catalysts (5–10 mol‐%) in the enantioselective reduction of prochiral ketones ( ee 72–86 %), giving the desired alcohols in satisfactory yields. We have theoretically investigated the mechanism of the reduction of chloroacetophenone at the DFT level and the computational results have provided a complete mechanistic picture, which explains the stereochemical outcome of the reaction. The B–BOXate complex binds both the reducing agent CATBH and the carbonyl compound, activating the former as a hydride donor and enhancing the electrophilicity of the latter. Moreover, the structure of two boron–BOX (BOXate) complexes has been confirmed by means of X‐ray diffraction techniques.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)