Intramolecular vs. intermolecular induction in the diastereoselective catalytic reduction of 17-oxo-steroids

Reiners, I.; Martens, Jürgen; Schwarz, S.; Henkel, H.

doi:10.1016/0957-4166(96)00211-x

Cited by 13 publications

(5 citation statements)

References 18 publications

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“…The chirality of the reduced products is just the opposite to that of the (R) alcohols generated in the enantioselective reduction of aromatic ketone catalyzed by the (4S)-CBS catalyst 1a with borane used as a source of hydrogen. Later, Huang et al [2], Reiners et al [3], and Trentmann et al [4] also reported the same results as those obtained by Li and Xie. The chiral cyclic sulfur-containing oxazaborolidine is of importance in enantioselective reduction.…”

supporting

confidence: 86%

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

Xie

et al. 2000

Int. J. Quantum Chem.

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ABSTRACT:In the present paper, the ab initio molecular orbital method is employed to study the structures of the adducts of borane and aromatic ketone to chiral cyclic sulfur-containing oxazaborolidine used as a catalyst in the enantioselective reduction of aromatic ketone. The catalyst-borane-ketone adducts have four different structures. All the structures are optimized completely by means of the Hartree-Fock method at 6-31g * basis sets. The structure which is of the greatest advantage to a hydride transfer from the borane moiety to the carbonyl carbon of aromatic ketone is the one with the next lowest formation energy, and the plausible transition state for the hydride transfer is predicted to be of a twisted boat structure.

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supporting

confidence: 86%

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

Xie

et al. 2000

Int. J. Quantum Chem.

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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%

“…19,[44][45][46] This sulfur-containing modification to the classical CBS catalyst leads to complete inversion of stereoselectivity, as shown independently by three experimental groups. [47][48][49][50] 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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“…Therefore, borane coordinates easily at the N(3) site. For the soft Lewis base S(7), according to the rule of hard-soft acids and bases proposed by Pearson [9], it may coordinate with the soft Lewis acid BH 3 . Since it has a positive charge, however, the trend of S(7) donating electrons to borane is also weak.…”

Section: The Cto Catalystmentioning

confidence: 99%

“…Because chiral cyclic sulfur-containing oxazaborolidine catalysts were reported first by Li and Xie [1], Huang et al [2], Reiners et al [3], and Trentmann et al [4], respectively, they are called for the purpose of convenient discussion, the Chengdu-Taipei-Oldenburg (CTO) catalysts herein. The CTO catalyst 1 is obtained by replacement of pyrrolidine with thiazolidine in the CBS catalyst 1a.…”

mentioning

confidence: 99%

Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 1. Structures and properties of catalysts

Xie

et al. 2000

Int. J. Quantum Chem.

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ABSTRACT:The ab initio molecular orbital method is employed to study the structures and properties of chiral cyclic sulfur-containing oxazaborolidine, as a catalyst, and its borane adducts. All the structures are optimized completely by means of the Hartree-Fock method at 6-31g * basis sets. The catalyst is a twisted chair structure and reacts with borane to form four plausible catalyst-borane adducts. Borane-sulfur adducts may be formed, but they barely react with aromatic ketone to form catalyst-borane-ketone adducts, because they are repulsed greatly by the atoms arising from the chair rear of the catalyst with a twisted chair structure. Borane-N adduct has the largest formation energy and is predicted to react easily with aromatic ketone to form catalyst-borane-ketone adducts. The formation of the catalyst-borane adducts causes the B BH3 -H BH3 bond lengths of the BH 3 moiety to be increased and thus enhances the activity of the enantioselective catalytic reduction. The borane-N adduct is of great advantage to hydride transfer.

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Intramolecular vs. intermolecular induction in the diastereoselective catalytic reduction of 17-oxo-steroids

Cited by 13 publications

References 18 publications

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

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

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

Quantum chemical study on enantioselective reduction of aromatic ketones catalyzed by chiral cyclic sulfur-containing oxazaborolidines. Part 1. Structures and properties of catalysts

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