The kinetic role of hydroxylic solvent in the reduction of ketones by sodium borohydride. New proposals for mechanism, transition state geometry, and a comment on the origin of stereoselectivity

Wigfield, Donald C.; Gowland, Frederick W.

doi:10.1021/jo00426a048

Cited by 53 publications

(28 citation statements)

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“…involving two molecules of solvent (1). consideration of other factors led to the suggestion that the axial Stereoisomer Piirification hydrogen at C-4 of a cyclohexanone might be playing…”

mentioning

confidence: 99%

The chemistry of 2-methyltetrahydropyran-4-one: An L-Selectride reaction that gives predominantly the equatorial alcohol

Wigfield¹,

Feiner²

1978

Can. J. Chem.

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The stereoisomers of 2-methyltetrahydropyran-4-ol have been separated and identified by carbon-13 and proton nmr analysis of the trideuteriomethyl-2,6,6-trideuterio analogue. Stereoisomeric product ratios of reduction of 2-methyltetrahydropyran-4-one (1) by NaBH4, KBH4, L-Selectride, K-Selectride, and LiBH(nBu)3 have been determined and compared with reductions of 3-methylcyclohexanone. Product ratios in the reduction of the two substrates by the borohydride reducing agents are similar but are quite different in the reduction by the Selectride reducing agents, 1 being reduced by Selectride to give 73% equatorialalcohol. Two possible mechanisms of reduction of 1 are proposed, involving intramolecular assistance by the cyclic ether oxygen.

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“…involving two molecules of solvent (1). consideration of other factors led to the suggestion that the axial Stereoisomer Piirification hydrogen at C-4 of a cyclohexanone might be playing…”

mentioning

confidence: 99%

The chemistry of 2-methyltetrahydropyran-4-one: An L-Selectride reaction that gives predominantly the equatorial alcohol

Wigfield¹,

Feiner²

1978

Can. J. Chem.

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“…14 The reduction of 25 in ethanol also exclusively gave a trans-diol, in which the hydride had attacked from the same side of the 2-axial hydroxy group. In this case a very slow generation of hydrogen gas, less than 10% of the theoretical amount, was observed during the addition of NaBH 4 under the reaction condition employed.…”

Section: Directive Effect Of the Hydroxy Group In The Cyclohexanone Smentioning

confidence: 99%

“…Geneste and Lamaty 13 postulated a four-centered cyclic transition state for reduction with LiAlH 4 , while Wigfield and Gowland 14 found participation of the solvent in NaBH 4 reductions by kinetic measurements. They proposed not the cyclic four-centered transition state but a linear one including solvent molecules.…”

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confidence: 99%

Role of the heteroatom on stereoselectivity in the complex metal hydride reduction of six‐membered cyclic ketones

Senda

2002

Chirality

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The role of the heteroatom on the stereochemistry and the relative rate for the complex metal hydride reduction of heteracyclohexanones and methoxy substituted cyclohexanones is explained by the difference in the nonbonding two electron stabilization between the incipient sigma* bond and the anti periplanar allylic sigma(i) bonds which were perturbed by the through space and/or through bond interaction with the remote heteroatom. A significant directive effect of the 2 axial hydroxyl group appears in the reduction of cyclohexanone with representative complex metal hydrides, while the 3 axial hydroxyl group exhibits a steric hindrance. The distance between the carbonyl carbon and the hydroxyl group which interacts with the hydride reagent is mainly responsible for such a difference. The key point of the extremely high directive effect appeared in the Na[B(OAc)(3)H] reduction for both 2 and 3 axial hydroxycyclohexanone is the formation of Na[B(OAc)(2)(OR)H], which is far more reactive than the parent hydride, by exchanging the acetate ion with the alkoxide.

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“…The term 'steric hindrance' needs t o be revised in view of the above considerations (8). The steric congestion in the vicinity of the carbonyl function with respect to the perpendicular approach of a nucleophile is not the same as when the angle of approach is wider (8,9). However, for reasons of simplicity, theoretical calculations generally assume a perpendicular approach (1 0).…”

Section: Metal Hydride Reductions Of the Carbonyl Functionmentioning

confidence: 99%

Reduction of cyclic anhydrides. II. Factors affecting regioselectivity of attack on the carbonyl group by metal hydrides

Kayser¹,

Morand²

1978

Can. J. Chem.

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. Can. J. Chem. 56,1524Chem. 56, (1978. The reduction of unsymmetrically substituted cyclic anhydrides with metal hydrides often leads to the preferential formation of one of the two possible lactones. In the light of recent experimental findings and theories concerning metal hydride addition t o the carbonyl function, the electronic and steric factors influencing regioselectivity of cyclic anhydride reductions are discussed and an explanation for the observed patterns is proffered. Similar considerations may be extended to predict the major lactonic products in the reductions of various other unsymmetrical cyclic anhydrides.MARGARET M. KAYSER et PETER MORAND. Can. J. Chem. 56,1524Chem. 56, (1978. La reduction par les hydrures metalliques d'anhydrides cycliques substitues d'une favon non-symetrique conduit souvent a la formation preferentielle d'une des deux lactones possibles. A la lumitke de resultats experimentaux recents et des theories concernant I'addition des hydrures mCtalliques sur les fonctions carbonyles, on discute des facteurs electroniques et steriques influen~ant la r6gioselectivite des reductions d'anhydrides cycliques et on presente une explication pour les tendances observees. On peut Ctendre des considerations similaires pour predire la nature des produits lactoniques principaux formis lors de la reduction de divers autres anhydrides cycliques non-symCtriques.[Traduit par le journal]The direct conversion of a cyclic anhydride into the corresponding lactone is of general interest to chemists, as it is well established that lactones are important intermediates in the synthesis of a variety of compounds, particularly natural products; see, for example, ref. la. Several methods have been used to accomplish this conversion (1 band c) but the simplest and most effective are reductions with metal hydrides. Unsymmetrically substituted anhydrides can potentially yield two lactones. Catalytic hydrogenations generally produce lactones resulting from the reduction of the less hindered carbonyl function (16). Reductions with metal hydrides, often but not always, take place selectively at t h e more hindered caibonyl group (2, 3). In this paper, an attempt is made to identify the factors which appear to govern regioselectivity in metal hydride reductions.Selective reduction of the more stericallv encumbered carbonyl group with metal hydridesdhas been explained by a mechanism involving initial attack of a metal cation o n the less hindered carbonyl function, followed by the transfer of a hydride ion to the more hindered carbonyl group (20 and b).' T h e intermediate aldehyde is then rapidly reduced t o yield an alcohol function and cyclization occurs upon acidification (Fig. 1). Although never challenged, the mechanism of Bloomfield and Lee (26) fails t o exlain known cases of referential reduction of the iess hindered carbonyl group (3c a n d a').In the course of our work on reductions of cyclic anhydrides, we have encountered other cases of 'Such selectivity has been reported in the reactions of steroida...

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The kinetic role of hydroxylic solvent in the reduction of ketones by sodium borohydride. New proposals for mechanism, transition state geometry, and a comment on the origin of stereoselectivity

Cited by 53 publications

References 1 publication

The chemistry of 2-methyltetrahydropyran-4-one: An L-Selectride reaction that gives predominantly the equatorial alcohol

The chemistry of 2-methyltetrahydropyran-4-one: An L-Selectride reaction that gives predominantly the equatorial alcohol

Role of the heteroatom on stereoselectivity in the complex metal hydride reduction of six‐membered cyclic ketones

Reduction of cyclic anhydrides. II. Factors affecting regioselectivity of attack on the carbonyl group by metal hydrides

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