Hartree Fock calculations on the effects of Lewis acids on the helimerization barrier of a lactone-bridged biaryl

Bringmann, Gerhard; Dauer, Ulrich; Kraus, Jürgen

doi:10.1016/s0040-4020(98)00755-8

Cited by 3 publications

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“…In recent papers we have presented quantum chemical studies on structures and dynamics of six-membered lactones such as 6 , , including the complete mechanistic course of the atropisomer-selective ring cleavage reaction of the configurationally unstable 1,3-dimethyl-6 H -benzo[ b ]naphtho[1,2- d ]pyran-6-one ( 6c ) with a chiral oxazaborolidine−BH 3 complex and with a chiral metalated N -nucleophile, using the semiempirical AM1 and PM3 methods, respectively. As in our previous computational studies on configurationally unstable six-membered lactones, we have subdivided the mechanistic course of the atroposelective ring cleavage of the configurationally stable seven-membered lactone 3 into five fundamental steps [Scheme , exemplarily for ( M )- 3 ], starting with the formation of the adduct 8 of 3 and the oxazaborolidine borane complex ( S )- 4 ·BH 3 (step I ), which is followed by the first intramolecular nucleophilic attack (step II ) of the activated hydride species to give lactolates of type 9 [here ( S , M )- 9 ].…”

Section: Resultsmentioning

confidence: 99%

Nondynamic Kinetic Resolution of Configurationally Stable Biaryl Lactones by Reduction with Oxazaborolidine-Activated Borane: AM1 Studies and Experimental Verification

et al. 2000

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The complete mechanistic course of the atroposelective ring opening of a lactone-bridged biaryl, dinaphth[2,1-c:1',2'-e]oxepin-3-(5H)-one (3), with a chiral oxazaborolidine-BH3 complex was calculated using the semiempirical AM1 method. The first hydride transfer to the activated carbonyl function of the adduct complexes was elaborated to be the selectivity-determining step in the postulated five-step mechanism. The calculated enantioselectivity is in good accordance with the experimental results, so that related calculations were performed on the atroposelective ring opening of a sterically strongly hindered and therefore also configurationally stable six-membered biaryl lactone, 1,3-di-tert-butyl-6H-benzo[b]naphtho[1,2-d]pyran-6-one (6f). These calculations predicted a highly (M)-selective reduction of 6f (kM/kP = 358 at -78 degrees C), which, after the smooth preparation of 6f by intramolecular biaryl coupling in high yields, was fully confirmed experimentally (kM/kP > 200 at -78 degrees C). Isolation of the intermediate hydroxy aldehyde (M)-14 at the beginning of the reaction with the same enantiomeric excess as found for the corresponding alcohol (M)-7f conclusively showed the first hydride transfer step to determine the selectivity of this process. The good agreement of computationally predicted and experimentally confirmed values proves the suitability of the AM1 method for mechanistic studies on even such complex reactions and opens a most efficient overall synthesis of sterically highly hindered biaryls, in excellent chemical (for the ring closure) and optical (for the ring cleavage) yields and for any desired axial configuration.

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Section: Resultsmentioning

confidence: 99%

Nondynamic Kinetic Resolution of Configurationally Stable Biaryl Lactones by Reduction with Oxazaborolidine-Activated Borane: AM1 Studies and Experimental Verification

et al. 2000

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“…Detailed structural investigations on a broad series of differently substituted lactones of type by semiempirical (AM1, PM3, MNDO) 61-64 and ab initio (HF and DF, with various basis sets) 61,65 calculations show that these bridged biaryls are not flat at all (not even for D, i.e. R = H), but helically distorted and hence chiral.…”

Section: Tpurrã(mentioning

confidence: 99%

The Lactone Concept: An Efficient Pathway to Axially Chiral Natural Products and Useful Reagents

1999

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$EVWUDFW A highly efficient concept for the stereoselective synthesis of axially chiral biaryl target molecules is presented: the atroposelective ring cleavage of configurationally unstable lactonebridged biaryls. The method has almost no restrictions concerning the substitution pattern, works even for substrates with high steric hindrance at the RUWKR-position(s) of the axis, and allows the optional, atropo-divergent preparation of each atropisomer from the same biaryl lactone precursor and a recycling of the undesired minor product in the sense of a chiral economy. A broad series of successful applications in natural product and ligand syntheses underlines the high value of the method. .H\ ZRUGV axial chirality, biaryl natural products, biaryl ligands and reagents, atropo-divergent synthesis, lactone-bridged biaryls '-BINAP' () R 7

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The lactone concept—a novel approach to the metal-assisted atroposelective construction of axially chiral biaryl systems

Bringmann

Breuning

Pfeifer

et al. 2002

Journal of Organometallic Chemistry

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Hartree Fock calculations on the effects of Lewis acids on the helimerization barrier of a lactone-bridged biaryl

Cited by 3 publications

References 11 publications

Nondynamic Kinetic Resolution of Configurationally Stable Biaryl Lactones by Reduction with Oxazaborolidine-Activated Borane: AM1 Studies and Experimental Verification

Nondynamic Kinetic Resolution of Configurationally Stable Biaryl Lactones by Reduction with Oxazaborolidine-Activated Borane: AM1 Studies and Experimental Verification

The Lactone Concept: An Efficient Pathway to Axially Chiral Natural Products and Useful Reagents

The lactone concept—a novel approach to the metal-assisted atroposelective construction of axially chiral biaryl systems

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