Asymmetric oxygenation of chiral imide enolates. A general approach to the synthesis of enantiomerically pure .alpha.-hydroxy carboxylic acid synthons

Evans, David A.; Morrissey, Michael M.; Dorow, Roberta L.

doi:10.1021/ja00300a054

Cited by 262 publications

(84 citation statements)

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“…[20][21][22][23][24][25][26][27] The majority of these reactions undergo acid catalysis and Evans and coworkers have proposed a mechanism to account for the reaction, as shown in Scheme 1. [5][6][7][8]11,12] The "unexpected" stereochemistry, considering the steric effects of the ring substituent, can be understood by assuming that the reacting conformer is the one in which the two carbonyl groups are coplanar as a result of their complexation with the Lewis acid (Scheme 1). [12] Subsequently, it was assumed that this was the explanation for all reactions in which this stereochemistry was obtained (almost all with experimental data, suggesting that this type of complex is not very probable, even with ligands having an appropriate carbonyl orientation.…”

Section: Introductionmentioning

confidence: 99%

A Theoretical Study of the Stereoselectivities of the Diels–Alder Addition of Cyclopentadiene to Ethyl‐(S)‐lactyl Acrylate Catalyzed by Aluminium Chloride

Bakalova

Santos

2006

Eur J Org Chem

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We have studied the AlCl 3 -catalyzed cycloaddition of ethyl-(S)-lactyl acrylate (ELA) and cyclopentadiene (CPD) by MP2 and DFT (B3LYP) methods using the 6-31G(d,p) basis set, with or without solvent effects. Four types of dienophileLewis acid (LA) complexes were considered − two types of ELA·AlCl 3 , ELA·2AlCl 3 and ELA·AlCl 2 + . The stereochemical predictions of these models were compared with available experimental data. The participation of lactate-bound ELA·AlCl 3 complexes is insignificant because of their relatively high TS energies. The diastereofacial selectivities exhibited by the chelated ELA·AlCl 2 + complex do not agree

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Section: Introductionmentioning

confidence: 99%

A Theoretical Study of the Stereoselectivities of the Diels–Alder Addition of Cyclopentadiene to Ethyl‐(S)‐lactyl Acrylate Catalyzed by Aluminium Chloride

Bakalova

Santos

2006

Eur J Org Chem

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“…The side chain can have destabilizing steric interactions with the ring carbonyl group and the ring substituent, which also reduces the number of possible conformers. [14,[16][17][18] If the side chain contains functional groups with the possibility of forming chelates with Lewis acids and the carbonyl groups, then we get another way to control the system rigidity. [12,16,18] Since the most important condition to achieve a high degree of stereocontrol in asymmetric synthesis is the rigidity of the transition state or, in another words, the low number of probable conformers, the properties of this system make it a very interesting chiral auxiliary.…”

Section: Introductionmentioning

confidence: 99%

New Chiral Auxiliaries for Dynamic Kinetic Resolution: From Theory to Experiment

Santos¹,

Pereira²,

Afonso³

et al. 2004

Chemistry A European J

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New efficient chiral auxiliaries for dynamic kinetic resolution (DKR) of bromides into amines are proposed, based on a theoretical rationalisation of known literature results. One example was synthesized and tested, affording diastereoselectivities up to 100%. Several results of DKR reactions are known, based on oxazolidinone or imidazolidinone units as chiral auxiliaries. Nevertheless, their behaviour was not fully understood until a recent paper that we published. We now used our proposed mechanism to rationalize the behaviour of other similar chiral auxiliaries and to propose small structure changes in imidazolidinone rings which could largely improve their performance. We could show that the good performance of these molecules as chiral auxiliaries for DKR reactions where bromine is the leaving group and a primary or secondary amine is the nucleophile is due, in a first step, to the formation of a hydrogen bond between the amine and the ring carbonyl oxygen and, in a second step, to the strong electrostatic interaction between the leaving bromide and the carbonyl oxygen in the C-3 substituent. Considering the behaviour of this substituent which rotates to minimize the electrostatic repulsion with the bromide when reaching the transition state, we proposed the introduction of a second substituent in the C-4 position of the imidazolidinone ring, which prevents such rotation, thus increasing the energy difference between the transition states of the two distereoisomers. With such an auxiliary we were able to increase the best de known in literature (88%), when benzylamine is used as nucleophile, to 99, or even 100%, when iodide replaces the bromide in the substrate.

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“…After conversion to a tosylate (95% yield), C-C bond elongation was accomplished by employing Me 2 CuLi, giving 16 in 78% yield. Hydrolysis of 16 (98% yield) followed by introduction of the S or R Evans's chiral auxiliary 11) gave 18 in 93% yield and 25 in 97% yield, respectively. The -hydroxylation of 18 and 25 by using MoOPH 12) stereoselectively proceeded to give 19 (43% yield, 17% recovered) and 26 (45% yield, 18% recovered), respectively.…”

Section: Resultsmentioning

confidence: 99%

Syntheses of (+)- and (−)-Dihydropinidine and (+)- and (−)-Epidihydropinidine by Using Yeast Reduction of Methyl (2-oxocyclohexyl)acetate

Yamauchi

Mori

Hirai

et al. 2004

Bioscience, Biotechnology, and Biochemistry

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Asymmetric oxygenation of chiral imide enolates. A general approach to the synthesis of enantiomerically pure .alpha.-hydroxy carboxylic acid synthons

Cited by 262 publications

References 0 publications

A Theoretical Study of the Stereoselectivities of the Diels–Alder Addition of Cyclopentadiene to Ethyl‐(S)‐lactyl Acrylate Catalyzed by Aluminium Chloride

A Theoretical Study of the Stereoselectivities of the Diels–Alder Addition of Cyclopentadiene to Ethyl‐(S)‐lactyl Acrylate Catalyzed by Aluminium Chloride

New Chiral Auxiliaries for Dynamic Kinetic Resolution: From Theory to Experiment

Syntheses of (+)- and (−)-Dihydropinidine and (+)- and (−)-Epidihydropinidine by Using Yeast Reduction of Methyl (2-oxocyclohexyl)acetate

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