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Quantum chemical study on enantioselective reduction of keto oxime ether with borane catalyzed by oxazaborolidine. Part 2. Structures of catalyst‐alkoxyborane adduct with a four‐membered ring and succeeding reaction intermediates
Author(s) -
Li Ming,
Zheng Wenxu,
He Rongxing,
Tian Anmin
Publication year - 2003
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.10534
Subject(s) - adduct , oxime , chemistry , borane , ring (chemistry) , catalysis , ether , enantioselective synthesis , stereochemistry , medicinal chemistry , computational chemistry , organic chemistry
Quantum chemical ab initio computations of the structures and properties of oxazaborolidine‐alkoxyborane adduct with a BNBO four‐membered ring and succeeding reaction intermediates are carried out in the current work by means of the Hartree–Fock (HF) and the density functional methods. All the structures are optimized completely at the HF/6‐31G(d) and Becke's three‐parameter exchange functional and the gradient‐corrected functional of Lee, Yang, and Paar (B3LYP)/6‐31G(d) levels. As shown in the obtained results, the oxazaborolidine‐alkoxyborane adduct with a BNBO four‐membered ring may be formed during the reduction of the carbonyl bond of the catalyst‐borane‐keto oxime ether adduct. The breakdown of the BNBO four‐membered ring results in the formation of the adduct with a BNBOCCN seven‐membered ring and an oxime bond. The reduction of the oxime bond leads to the adduct with a chiral oxime carbon. The B(2)N CN bond in the BNBOCCN seven‐membered ring of the adduct with a reduced oxime bond is weaker comparatively and thus may be more easily broken down. All the adducts have four stable structures. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 294–306, 2003