Temperature- and electrophile-dependent stereocontrol: A structural and mechanistic investigation of (-)-sparteine-mediated asymmetric lithiation- substitution sequences of N-Boc-N-(p-methoxyphenyl)cinnamylamine

Journal of the American Chemical Society

Volumn 121, Issue 41, 1999, Pages 9522-9530

  Weisenburger, Gerald A ^a   Faibish, Neil C ^a   Pippel, Daniel J ^a   Beak, Peter ^a  

^a UNIVERSITY OF ILLINOIS AT URBANA CHAMPAIGN   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

PENTYLAMINE; SPARTEINE;

ARTICLE; CARBON NUCLEAR MAGNETIC RESONANCE; CHEMICAL STRUCTURE; ENANTIOMER; REACTION ANALYSIS; SEQUENCE ANALYSIS; STEREOCHEMISTRY; STRUCTURE ANALYSIS; TEMPERATURE DEPENDENCE;

EID: 0032706536     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja9910560     Document Type: Article

References (45)

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14. 1,4
15. The allylic organolithium complexes described herein are designated according to (1) the face of the allyl unit which bears the lithium, exo or endo, and (2) the relationship between the H atom at C-2 of the allyl unit and the non-H substituents at C-3 and C-1, anti or syn. (Matrix Presented)
16. Absolute configurations for (Z,S)-9 and (Z,S)-11 were obtained through hydrolysis and conversion to the corresponding α-methylbenzylamine propionamides which are crystallographically known; see ref 3b.
17. The organolithium generated from (E)-2 does not react with TMSCl at -78 °C.
18. 1 (see Supporting Information for details).
19. (a) An additional weak absorption, present at 0.26 ppm, may be ascribed to one or both of the syn-syn isomers. (b) An additional weak absorption appears at 82.7 ppm. Based on evidence from our subsequent study on the lithiodestannylation of (E)-rac-12 (Figure 1d), this peak is ascribed to one of the allylic terminal carbons of a syn-syn-8·1 isomer. The other allylic syn-syn terminal peak is presumed to be at 80.7, accidentally equivalent with a peak from exo-syn-anti-8·1.
20. 13C NMR data is attributed to partial equilibration of the diastereomeric complexes caused by warming during removal from the NMR spectrometer. The enantiomeric ratio of the minor product (E,R)-11 was not determined.
21. Apparent fine structure in the peak at 82.7 ppm may represent partial separation of endo-syn-syn-8·1 and exo-syn-syn-8·1.
22. Experimentally, at -78 °C, the Z/E product ratios are reduced when starting with (E)-12 versus (E)-2. This suggests that (E)-rac-12 undergoes transmetalation from two conformations competitively to give both racemic syn-anti-8 and syn-syn-8. (Matrix Presented)
23. 13C coupling was observed.
24. 1 species which equilibrate rapidly and stereoselectively are present. (Matrix Presented)
25. 1 species which equilibrate rapidly and stereoselectively are present. (Matrix Presented)
26. 1 species which equilibrate rapidly and stereoselectively are present. (Matrix Presented)
27. For details on the effect of ligand on configurational stability, see the Supporting Information.
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44. 6c
45. The erosion of er from 97:3 in (E,S)-12 to 88:12 in (Z,R)-11 could indicate that the reaction between benzyl bromide and exo-syn-anti-8·1 is less stereoselective than that between benzyl bromide and endo-syn-anti-8·1. Alternatively, it might indicate that the lithiodestannylation does not occur with complete retention of configuration at carbon.