Enantioselective catalytic ring expansion of methylenecyclopropane carboxamides promoted by a chiral magnesium lewis acid

Organic Letters

Volumn 9, Issue 4, 2007, Pages 591-593

  Taillier, Catherine ^a   Lautens, Mark ^a  

^a UNIVERSITY OF TORONTO   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 33847786262     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol0628614     Document Type: Article

References (14)

1. (a) Lautens, M.; Han, W. J. Am. Chem. Soc. 2002, 124, 6312-6316.
2. (b) Scott, M. E.; Han, W.; Lautens, M. Org. Lett. 2004, 6, 3309-3312.
3. 2 for ring opening of cyclopropyl derivatives, see: Alper, P. B.; Meyers, C.; Lerchner, A.; Siegel, D. R.; Carreira, M. E. Angew. Chem., Int. Ed. 1999, 38, 3186-3189.
4. For reviews on the use of oxazoline-containing ligands in asymmetric catalysis, see: (a) Ghosh, A. K.; Mathivanan, P.; Cappiello, J. Tetrahedron: Asymmetry 1998, 9, 1-45.
5. (b) McManus, H.; Guiry, P. J. Chem. Rev. 2004, 104, 4151-4202.
6. For an early report of the use of a bis(oxazoline)-Mg complex, see: Corey, E. J.; Ishihara, K. Tetrahedron Lett. 1992, 33, 6807-6810.
7. 2-mediated ring expansion usually affords mixtures of diastereomers depending on the substitution pattern of the aldimines. However, when the reaction was performed in the presence of bis(oxazoline) ligand 6c, only traces of the cis diastereomer were observed.
8. (a) Davies, I. E.; Gerena, L.; Castonguay, L.; Senanayake, C. H.; Larsen, R. D.; Verhoeven, T. R.; Reider, P. J. Synth. Commun. 1996, 1753-1754.
9. (b) Davies, I. E.; Deeth, R. J.; Larsen, R. D.; Reider, P. J. Tetrahedron Lett. 1999, 40, 1233-1236.
10. Other conditions, such as solvent, temperature, concentration, and quantity of the chiral complex, were also tested, but these reaction conditions were found to give the optimal balance of reaction yields and enantio-selectivity.
11. 2-mediated ring expansion of MCP 1 with the chiral p-methoxy-substituted aromatic sulfinime. After oxidation with m-CPBA, it was possible to assign the absolute configuration of the ring-expanded product 8i to be (2R,3K) by comparison of both optical rotations and chiral HPLC retention times (see Supporting Information).
12. The absolute configuration of the other products was assigned in analogy to 8i.
13. L*) was found to be linear showing that diastereomeric dimeric species are not involved in the catalytic process. Kagan, H. B. Synlett 2001, 888-899.
14. Only traces of cis-pyrrolidines were occasionally detected in reaction mixtures.