Nonequilibrium radical reductions

Journal of the American Chemical Society

Volumn 120, Issue 22, 1998, Pages 5589-5590

  Buckmelter, Alexandre J ^a   Powers, Jay P ^a   Rychnovsky, Scott D ^a  

^a UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

RADICAL;

CONFORMATIONAL TRANSITION; DECARBOXYLATION; LETTER; REDUCTION; STEREOCHEMISTRY; SYNTHESIS;

EID: 0032503553     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja980857k     Document Type: Article

References (33)

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19. (b) Rychnovsky, S. D.; Dahanukar, V. H. J. Org. Chem. 1996, 61, 7648-9.
20. Certain reductive lithiations of 2-phenylthiotetrahydropyrans appear to be too selective when the energy of each radical conformer is considered: Powers, J. P. Ph.D. Thesis, University of Minnesota, 1995.
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24. The pseudo-A-value for a 3-methyl substituent on a THP ring is 1.43 kcal/mol (ref 13).
25. Molecular modeling (MM2) predicts that the axial nitrile conformations of 1ax and 1eq will be preferred by > 1.5 kcal/mol. The chemical shifts and ring coupling constants for 1ax and 1eq are essentially invariant between -70 and 25 °C, suggesting that only a single ring conformation is populated under these conditions.
26. The relative configurations of starting materials and products were assigned by coupling constant and NOE anaylsis as described in the Supporting Information.
27. Rychnovsky, S. D.; Zeller, S.; Skalitzky, D. J.; Griesgraber, G. J. Org. Chem. 1990, 55, 5550-1. Modeling (MM2 and AM1) suggests that only one of the two cyanohydrin acetonide diastereomers exists in a chair conformation. Reduction of both diastereomers lead to the cis product.
28. MM2 modeling of the methyl esters corresponding to 4ax and 4eq shows a >1.0 kcal/mol preference for the axial ester conformation.
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31. The Sax isomer adopts the conformation with the benzyl equatorial, but is drawn with the benzyl axial to emphasize its origins.
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