Influence of hydroxylamine conformation on stereocontrol in Pd-catalyzed isoxazolidine-forming reactions

Journal of Organic Chemistry

Volumn 74, Issue 6, 2009, Pages 2533-2540

  Lernen, Georgia S ^a   Giampietro, Natalie C ^a   Hay, Michael B ^a   Wolfe, John P ^a  

^a UNIVERSITY OF MICHIGAN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

ALKENYL; BOC GROUPS; BOND-FORMING; CONFORMATIONAL EQUILIBRIUM; DIASTEREO SELECTIVITIES; DIPOLAR CYCLOADDITION REACTIONS; GOOD YIELDS; HYDROXYLAMINE DERIVATIVES; ISOXAZOLIDINE; ISOXAZOLIDINES; PERPENDICULAR ORIENTATIONS; STEREOCONTROL; TRANSITION STATE;

AMINES; BROMINE COMPOUNDS; CYCLOADDITION; FORMING; PALLADIUM;

REACTION KINETICS;

ALKENE; DEUTERIUM; HYDROXYLAMINE; ISOXAZOLIDINE DERIVATIVE; LIGAND; PALLADIUM;

AMINATION; ARTICLE; CARBOAMINATION; CARBOETHERIFICATION; CHEMICAL STRUCTURE; CONFORMATIONAL TRANSITION; CYCLOADDITION; ETHERIFICATION; STEREOCHEMISTRY; SYNTHESIS;

AMINATION; CATALYSIS; CYCLIZATION; HYDROXYLAMINE; MOLECULAR CONFORMATION; OXAZOLES; PALLADIUM; STEREOISOMERISM;

EID: 64149126749     PISSN: 00223263     EISSN: None     Source Type: Journal    
DOI: 10.1021/jo8027399     Document Type: Article

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32. Chen has reported that reactions of 4c with bromobenzene in the presence of various ligands proceed with the following diastereoselectivities (trans:cis): (a) Dpe-phos, 2:1;
33. (b) Xantphos, 1:2;
34. 3P, 1:1;
35. (d) dppf, 1:1;
36. (e) BINAP, 1:1. See ref 9. We have observed that three reactions of 4c with different aryl bromides all proceed with 3 to 4:1 dr when Dpe-phos is used as ligand. See ref 8 and Table 4, entry 1.
37. 2O.
38. The enantiomerically enriched alcohol was prepared via lipase-catalyzed kinetic resolution of racemic 1-phenylbut-3-en-2-ol. See: Chalecki, Z.; GuibéJampel, E.; Plenkiewicz, J. Synth. Commun. 1997, 27, 1217-1222.
39. The small difference between enantiomeric purity of the product (97% ee) and the substrate (96% ee) is likely due to small errors in the integration of HPLC traces.
40. The Pd-catalyzed carboamination reactions of 33 also generated significant amounts of 1-phenylbut-3-en-1-ol and other side products resulting from substrate N-O bond cleavage. Control experiments indicated that the N - O bond cleavage occurred upon heating the substrate in the presence of NaOtBu with no palladium catalyst.
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47. The observation that most ligands examined provide ca. 1 - 2:1 dr in the reaction of 4c with bromobenzene is also consistent with a very small difference in energy between these two transition states. See ref 9 and footnote 19.
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59. This effect would also be expected to raise the energy of transition state 49 leading to the minor diastereomer. However, it does not appear that the energy of 48, which also leads to the minor diastereomer, would be significantly perturbed.
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