Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 2. Structures of catalyst-borane-ketone adducts

Li, Ming; Xie, Ruili; Hu, Xairong; Tian, Anmin

doi:10.1002/(sici)1097-461x(2000)78:4<252::aid-qua7>3.0.co;2-n

Cited by 7 publications

(3 citation statements)

References 13 publications

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“…In their studies of pinacolone reduction, , Tian and Li describe borane−catalyst−substrate ternary complexes and the oxazadiboretane species corresponding to the intermediate product from hydride transfer. No calculation is reported about transition states in those papers nor in those dealing with a modified CBS catalyst containing a sulfur atom instead of the central methylene unit of the proline ring (in this case as well, the 5,5‘-diphenylic substituent is omitted). ,− This sulfur-containing modification to the classical CBS catalyst leads to complete inversion of stereoselectivity, as shown independently by three experimental groups. − A more detailed description, with full characterization of the transition states for the competing reaction pathways, would have been useful for explaining this interesting phenomenon.…”

Section: Introductionmentioning

confidence: 99%

Quantum Mechanical Study of Stereoselectivity in the Oxazaborolidine-Catalyzed Reduction of Acetophenone

et al. 2003

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Chiral oxazaborolidines, known as CBS catalysts after the work of Corey, Bakshi and Shibata, are used for the stereoselective reduction of prochiral ketones to secondary chiral alcohols. Due to their relative low cost, ease of use, and high selectivity, their popularity has remarkably grown in the last 15 years. Oxazaborolidine-catalyzed reductions have been much studied, both experimentally and computationally, by means of semiempirical methods. Though, a more accurate high level quantum mechanical study on the complete system, capable of elucidating reliably the origins of stereoselectivity, is still lacking. Therefore, the acetophenone (PhMK) reduction with Corey's oxazaborolidine has been modeled for the first time with ab initio and DFT-B3LYP calculations on the complete system as well as with AM1. Calculations on the complexation of BH(3) to CBS, which can occur only in a cis fashion with respect to the hydrogen on the stereogenic C-4 carbon atom, have allowed us to confirm the great rigidity of Corey's catalyst, possibly determining its excellent enantioselectivity. Acetophenone-CBS-BH(3) complexes were characterized at various levels of theory, and it was found that the picture obtained depends heavily on the method adopted. A computational strategy for identifying the hydride transfer transition states of the competing pathways was developed and tested, using a model system for which the transition state geometry was already known. The application of the TS search method to the reduction of acetophenone allowed the characterization of the TS's for the competing pathways in this reaction, making it possible to predict with good quantitative accuracy the stereochemical outcome of the reaction at all the levels of theory adopted. The characterization of the intermediate oxazadiboretane products confirmed that the highly exothermic hydride transfer provides the thermodynamical drive for the reaction.

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Section: Introductionmentioning

confidence: 99%

Quantum Mechanical Study of Stereoselectivity in the Oxazaborolidine-Catalyzed Reduction of Acetophenone

et al. 2003

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“…The formation of an oxazadiboretane intermediate product (see Scheme ) was predicted in Corey's model 45 and has been experimentally observed through low-temperature NMR investigations . Besides, this intermediate has been described in a number of theoretical calculations. ,,,, Dissociation to regenerate the catalyst and form an alkoxyborane may occur by two different reaction mechanisms: cycloelimination or borane addition. In the second case, a six-membered bridged species is formed that decomposes to the catalyst−borane complex and the alkoxyborane.…”

Section: Resultsmentioning

confidence: 94%

“…Theoretical computations on oxazaborolidine-catalyzed reduction of ketones have been reported by several authors. Most of the theoretical work has been carried out by Nevalainen. − Other contributions are due to Jones and Liotta, Bach et al, Linney et al, Quallich et al, Bringmann et al, , Göndös and Pálinkó, and Li et al. − A thorough survey of all these previous investigations has been recently reported by Alagona et al in this journal, and therefore we shall not comment on them in detail here (though some essential points are discussed below). In the work of Alagona et al, the authors have carried out ab initio density functional and semiempirical calculations for the system acetophenone + CBS catalyst + BH 3 .…”

Section: Introductionmentioning

confidence: 99%

A Model for Double Asymmetric Induction in the Stereocontrolled Reduction of Glycosyl α-Ketoesters with Oxazaborolidines

Harb¹,

Mf²,

Coutrot³

et al. 2004

J. Am. Chem. Soc.

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Experimental diastereoselectivities for the stereocontrolled reduction of glycosyl alpha-ketoesters into the corresponding alpha-hydroxyesters have recently been reported with unexpected results. The process is catalyzed by a chiral oxazaborolidine derivative (the so-called CBS catalyst) and represents the key step in the synthesis of glycosyl alpha-amino acids synthons, a class of compounds that allow preparation of natural glycopeptides analogues exhibiting potential therapeutic relevance. Good to very good diastereomeric excesses have been obtained for a series of reactions with different glucidic derivatives, but surprisingly, the major product obtained does not correspond to that predicted by using Corey's model. In the present work, we carry out a theoretical investigation of these reactions at the density functional level. Separated effects from the catalyst and from the glucidic derivative have been computed to rationalize the observed diastereoselectivities and the double asymmetric induction.

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Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 3. Structures of catalyst-alkoxyborane adducts

Xie

et al. 2000

Int. J. Quantum Chem.

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Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 2. Structures of catalyst-borane-ketone adducts

Cited by 7 publications

References 13 publications

Quantum Mechanical Study of Stereoselectivity in the Oxazaborolidine-Catalyzed Reduction of Acetophenone

Quantum Mechanical Study of Stereoselectivity in the Oxazaborolidine-Catalyzed Reduction of Acetophenone

A Model for Double Asymmetric Induction in the Stereocontrolled Reduction of Glycosyl α-Ketoesters with Oxazaborolidines

Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 3. Structures of catalyst-alkoxyborane adducts

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