Rationalising diastereoselection in the dynamic kinetic resolution of α-haloacyl imidazolidinones

Caddick, Stephen; Jenkins, Kerry; Treweeke, Nigel R.; Candeias, Sara X.; Afonso, Carlos A. M.

doi:10.1016/s0040-4039(98)00175-0

Cited by 22 publications

(10 citation statements)

References 14 publications

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“…31 The results described herein for the (4+3) cycloadditions of 2 Ph likely hold relevance to stereocontrol in these other oxazolidinone-directed reactions.…”

Section: Discussionmentioning

confidence: 76%

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

et al. 2011

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A systematic investigation of the regioselectivities and stereoselectivities of (4+3) cycloadditions between unsymmetrical furans and a chiral oxazolidinone-substituted oxyallyl is presented. Cycloadditions were performed using an oxyallyl containing a (R)-4-phenyl-2-oxazolidinone auxiliary (2Ph), under either thermal or ZnCl2-catalyzed conditions. Reactions of 2Ph with 2-substituted furans gave syn cycloadducts selectively, while cycloadditions with 3-substituted furans gave selectively anti cycloadducts. The stereoselectivities were in favor of a single diastereoisomer (I) in all but one case (2-CO2R). Density functional theory calculations were performed to explain the selectivities. The results support a mechanism in which all cycloadducts are formed from the E isomer of the oxyallyl (in which the oxazolidinone C=O and oxyallyl oxygen are anti to each other) or the corresponding E ZnCl2 complex. The major diastereomer is derived from addition of the furan to the more crowded face of the oxyallyl. Crowded transition states are favored because they possess a stabilizing CH–π interaction between the furan and the Ph group.

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“…31 The results described herein for the (4+3) cycloadditions of 2 Ph likely hold relevance to stereocontrol in these other oxazolidinone-directed reactions.…”

Section: Discussionmentioning

confidence: 76%

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

et al. 2011

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“…Theoretical studies: In our previous paper [19] we proposed a reaction mechanism for Caddicks system [32,41] based on calculated transition states at HF/3-21G*. The results were enthalpic values (DH), calculated by subtracting the enthalpy of the amine complex from that of the transition state ( Figure 3).…”

Section: Resultsmentioning

confidence: 99%

“…A second amine would make another hydrogen bond, directing the attack through the less hindered face. [32] Our involvement in Caddicks work brought us to another proposal [19,41] where an interaction between the leaving group (bromide) and the aromatic ring in the auxiliary moiety ( Figure 2) can explain all the experimental observations; this would avoid the need for the formation of a rather unlikely complex as that in Scheme 4.…”

Section: Introductionmentioning

confidence: 96%

“…In accordance with this, nucleophiles which are not capable of hydrogen bonding yielded the "expected" stereochemistry. [37][38][39] A few years ago, Caddick et al [31,32] found that the treatment of compound 6 with primary or secondary amines under DKR conditions similar to those used by Nunami yielded epimer 7 (2'R) (Scheme 4), which is again the unexpected isomer. Since there is no possibility for hydrogen bonding as suggested by Nunami, Caddick proposed a different mechanism where a hydrogen bond between the amine and the two carbonyl groups would shift the equilibrium from the anti-to the coplanar conformation (Scheme 4).…”

Section: Introductionmentioning

confidence: 97%

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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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“…[4][5][6][7][8][9][10][11][12] Oxazolidinones or imidazolidinones can be used as chiral auxiliaries in ionic, [10,13,14] radical [15][16][17][18][19] or even in dynamic kinetic resolution (DKR) reactions. [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).…”

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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Rationalising diastereoselection in the dynamic kinetic resolution of α-haloacyl imidazolidinones

Cited by 22 publications

References 14 publications

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

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

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

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