Tandem catalytic asymmetric ring-opening metathesis/ring-closing metathesis [14]

Journal of the American Chemical Society

Volumn 122, Issue 8, 2000, Pages 1828-1829

  Weatherhead, Gabriel S ^a   Ford, J Gair ^a   Alexanian, Erik J ^a   Schrock, Richard R ^b   Hoveyda, Amir H ^a  

^a BOSTON COLLEGE   (United States)

^b MASSACHUSETTS INSTITUTE OF TECHNOLOGY   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

CYCLOALKENE; MOLYBDENUM COMPLEX;

CATALYSIS; CHIRALITY; COMPLEX FORMATION; ENANTIOMER; GEL CHROMATOGRAPHY; LETTER; POLYMERIZATION; STEREOCHEMISTRY; SYNTHESIS;

EID: 0034053137     PISSN: 00027863     EISSN: None     Source Type: Journal    
DOI: 10.1021/ja993681a     Document Type: Letter

References (20)

1. La, D. S.; Ford, G. J.; Sattely, E. S.; Schrock, R. R.; Hoveyda, A. H. J. Am. Chem. Soc. 1999, 121, 11603-11604.
2. (a) Alexander, J. B.; La, D. S.; Cefalo, D. R.; Hoveyda, A. H.; Schrock, R. R. J. Am. Chem. Soc. 1998, 120, 4041-4042.
3. (b) La, D. S.; Alexander, J. B.; Cefalo, D. R.; Graf, D. D.; Hoveyda, A. H.; Schrock, R. R. J. Am. Chem. Soc. 1998, 120, 9720-9721.
4. Zhu, S.; Cefalo, D. R.; La, D. S.; Jamieson, J. Y.; Davis, W. M.; Hoveyda, A. H.; Schrock, R. R., J. Am. Chem. Soc. 1999, 121, 8251-8259.
5. For a recent review on catalytic metathesis, see: Grubbs, R. H.; Chang, S. Tetrahedron 1998, 54, 4413-4450.
6. For related non-asymmetric transformations, see: Zuercher, W. J.; Hashimoto, M.; Grubbs, R. H. J. Am. Chem. Soc. 1996, 118, 6634-6640.
7. The metal complex bears a chiral ligand, and there are stereogenic centers within the chain that undergoes cyclization. Thus, the combination of metal-center and chain chirality may prove to be mismatched (slow closure) or matched (fast closure). This was exploited in the Mo-catalyzed kinetic resolution processes (ref 2).
8. The constitutional and stereochemical identities of 5a and 5b were determined by comparison to authentic materials, prepared through a 10-step enantioselective synthesis (see the Supporting Information). The stereochemical outcomes of 10a and 10b, involving exo face addition, are by inference.
9. Complex 2 is typically less effective in promoting the catalytic AROM/ RCM discussed here (e.g., 11a is formed with 30% conv).
10. It is unlikely that with substrates in Table 1, reaction of the Mo-alkylidenes at the terminal olefins (reversible) leads to a productive pathway. The subsequent ARCM should prove prohibitive; not only are the cyclobutene and norbornene olefins substantially more reactive (particularly where 1,1-disubstituted alkenes are involved), but the requisite metallacyclobutanes would also be highly strained.
11. The stereochemical identity of 13 was determined through correlation with a closely related compound, the stereochemistry of which was determined by X-ray crystallography. See the Supporting Information.
12. (a) Harrity, J. P. A.; La, D. S.; Cefalo, D. R.; Visser, M. S.; Hoveyda, A. H. J. Am. Chem. Soc. 1998, 120, 2343-2351.
13. (b) Johannes, C. W.; Visser, M. S.; Weatherhead G. S.; Hoveyda, A. H. J. Am. Chem. Soc. 1998, 120, 8340-8347.
14. The stereochemical identity of 18 was established through comparison with authentic materials prepared through a seven-step independent synthesis. See the Supporting Information.
15. Reaction of 12 in the presence of 14 (Table 2, entry 3) may partially proceed via a similar triene intermediate (ARCM rather than AROM). However, the data in entry 1 of Table 2 indicate that catalytic AROM can occur with enantioselection, since the formation of the purported triene intermediate (cf. 17) requires the presence of a terminal alkene or ethylene. With 3a and 10a, reaction of the intermediate alkylidene (e.g., 4, Scheme 1) with a substrate molecule may lead to the formation of the derived tetraene which could undergo ARCM. In such cases, intermolecular reaction of the alkylidene with the substrate's more reactive cyclic olefin (vs a terminal alkene) would be expected to predominate, leading to oligomerization.
16. The first catalytic cycle is initiated by the original neophylidine complex, unless ethylene is present (or by addition of 14). Similar arguments as in Scheme 3 can be applied to the initial neophylidenes.
17. Schrock, R. R. Top. Organomet. Chem. 1998, 1, 1-36 and references therein.
18. On the basis of the identity of the product enantiomer and the model presented in Scheme 3, the approach of the chiral Mo-methylidene to the cyclic alkene of 12 occurs from the bicycle's endo face. This is presumably because the exo face is sterically rendered less accessible by the bridgehead alkoxide. Detailed mechanistic studies are in progress.
19. For a recent application of Mo-catalyzed ARCM to natural product synthesis, see: Burke, S. D.; Muller, N.; Beaudry, C. M. Org. Lett. 1999, 1, 1827-1829.
20. This research was supported by the NSF (CHE-9905806 to A.H.H.) and the NIH (GM-47480 to A.H.H.).