High stereochemical fidelity in reactions of an atropisomeric N- acyliminium intermediate

Synlett

Volumn , Issue 3, 2000, Pages 388-390

  Godfrey, Christopher R A ^a   Simpkins, Nigel S ^b   Walker, Matthew D ^b  

^a JEALOTT S HILL RESEARCH STATION   (United Kingdom)

^b UNIVERSITY OF NOTTINGHAM   (United Kingdom)

Author keywords

Allylations; Atropisomerism; Chiral auxiliaries; Lactams; N acyliminium

Indexed keywords

2 PYRROLIDONE DERIVATIVE; AMIDE; LACTAM; MENTHOL; TRIMETHYLSILYL DERIVATIVE;

ACYLATION; ALKYLATION; ARTICLE; CHEMICAL BOND; CHEMICAL REACTION; ENANTIOMER; HIGH PERFORMANCE LIQUID CHROMATOGRAPHY; MOLECULAR MODEL; NUCLEAR MAGNETIC RESONANCE; POLYMERIZATION; REACTION ANALYSIS; REDUCTION; STEREOCHEMISTRY; X RAY CRYSTALLOGRAPHY;

EID: 0034009416     PISSN: 09365214     EISSN: None     Source Type: Journal    
DOI: None     Document Type: Article

References (16)

1. (a) Hughes, A. D.; Price, D. A.; Shishkin, O.; Simpkins, N. S. Tetrahedron Lett. 1996, 37, 4607.
2. (b) Hughes, A. D.; Price, D. A.; Simpkins, N. S. J. Chem. Soc., Perkin Trans. 1 1999, 1295.
3. For the seminal contribution in this area, see Curran, D. P.; Qi, H.; Geib, S. J.; DeMello, N. C. J. Am. Chem. Soc. 1994, 116, 3131. See also reference 3 and references therein.
4. Fujita, M.; Kitagawa, O.; Izawa, H.; Dobashi, A.; Fukaya, H.; Taguchi, T. Tetrahedron Lett. 1999, 40, 1949.
5. This problem is discussed in a full account by Curran and co-workers, see Curran, D. P.; Hale, G. R.; Geib, S. J.; Balog, A.; Cass, Q. B.; Degani, A. L. G.; Hernandes, M. Z.; Freitas, L. C. G. Tetrahedron:Asymmetry 1997, 8, 3955.
6. For a recent relevant review and leading references on N-acyliminium chemistry, see de Koning, H.; Hiemstra, H.; Moolenaar, M. J.; Speckamp, W. N. Eur. J. Org. Chem. 1998, 1729.
7. 1/2 of ca. 6 months at - 40°C).
8. 3).
9. We thank Dr A. J. Blake of this School for this result, the full details will be published elsewhere.
10. The stereochemistry of compound 10 is assigned as shown based on thermal equilibration studies in which both 9 and 10 were each shown to interconvert with another isomer, but not with each other. In the subsequent substitution chemistry shown in Scheme 4 compound 10 gave enantiocomplementary results to those for 9.
11. 3SiCN or the enol silane derived from acetophenone, the simpler derivative 4 (LG = OMe) gave high yields of adduct. This suggests that the bulky menthol leaving group has a detrimental effect on the N-acyliminium compared to a methoxy group.
12. 1PrOH in hexane as eluant, and a flow rate of 1 ml/min, allowed separation of all four isomers. Starting with 9 gave two atropisomers of 13 eluting at 21.2 and 29.0 min, whereas starting with 10 gave two atropisomers eluting at 22.8 and 24.8 min.
13. 3
14. This effect seems to be thermodynamic rather than kinetic in origin since molecular modelling indicates that the two atropisomers of 3 should equilibrate readily at room temperature.
15. 2 requires M, 401.2930). The assignment of stereochemistry in this series relies solely on the observation that the product in Scheme 7 is (+)-16,and assumes analogous behaviour to that proved for 9 and 10.
16. Meyers, A. I.; Burgess, L. E. J. Org. Chem. 1991, 56, 2294.