Theoretical rationale for regioselection in phosphine-catalyzed allenoate additions to acrylates, imines, and aldehydes

Organic Letters

Volumn 8, Issue 17, 2006, Pages 3643-3646

  Dudding, Travis ^a   Kwon, Ohyun ^b   Mercier, Evan ^a  

^a BROCK UNIVERSITY   (Canada)

^b UNIVERSITY OF CALIFORNIA   (United States)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 33748632920     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol061095y     Document Type: Article

References (25)

1. For recent reviews, see: (a) Methot, J. L.; Roush, W. R. Adv. Synth. Catal. 2004, 346, 1035-1050.
2. (b) X. Lu, C. Zhang, Z. Xu, Acc. Chem. Res. 2001, 34, 535-544 and references therein.
3. Zhang, C.; Lu, X. J. Org. Chem. 1995, 60, 2906-2908. To facilitate computation, methyl 2,3-butadienoate and trimethylphosphine were substituted for reagents ethyl 2,3-butadienoate and tributylphosphine used experimentally.
4. Xu, Z.; Lu, X. J. Org. Chem. 1998, 63, 5031-5041. For reasons of computational efficiency trimethylphosphine was used instead of tributylphosphine for the calculation of imine regioselectivity.
5. Recently one of our groups has reported a variant of these reactions that affords exclusively six-membered tetrahydropyridines of γ-addition; see: Zhu, X.-F.; Lan, J.; Kwon, O. J. Am. Chem. Soc. 2003, 125, 4716-4717. Expanding upon this earlier work, Wurz and Fu have developed a catalytic enantioselective methodology for the preparation of chiral piperidine derivatives;
6. see: Wurz, R. P.; Fu, G. C. J. Am. Chem. Soc. 2005, 127, 12234-12235.
7. To our knowledge this is the first reported example of a phosphine-catalyzed addition of allenoates to aldehydes; see: Zhu, X.-F. Henry, C. E.; Wang, J.; Dudding, T.; Kwon, O. Org. Lett. 2005, 7, 1387-1390.
8. (a) Becke, A. D. J. Chem. Phys. 1993. 98, 5648-5652.
9. (b) Stephens, P. J.; Devlin, F. J.; Chabalowski, G. C.; Frisch, M. J. J. Phys. Chem. 1994, 98, 11623-11627.
10. (c) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1987, 37, 785-789.
11. (a) Clark, T.; Chandrasekhar, J.; Spitznagel, G. W.; Schleyer, P. v. R. J. Comput. Chem. 1983, 4, 294-301.
12. (b) Frisch, M. J.; Pople, J. A.; Binkley, J. S. J. Chem. Phys. 1984, 80, 3265-3269.
13. See Supporting Information for a complete list of authors of these programs.
14. To further validate experiment, we are currently investigating the regiochemical outcome of these additions when triphenylphosphine is used in place of trimethylphosphine. In addition a full disclosure of the reaction pathways of phosphine-mediated [2 + 2 + 2] aldehyde and [3 + 2] imine/acrylates additions will be reported by our groups shortly.
15. Low energy transition state structures for acrylate, imine, and aldehyde additions were located through potential energy surface (PES) scans.
16. For ring closure transition states α-TS4 and γ-TS4, see Supporting Information.
17. Ground-state optimization of the possible enolate geometries revealed that the (Z)-isomeric configuration between the ester and phosphonium groups is energetically preferred; see Supporting Information. For a discussion on the divergent reactivity of the (E)- and (Z)-configurations of zwitterionic intermediate 1↔2, see: Zhu, X.-F.; Schaffner, A.-P.; Li, R. C.; Kwon, O. Org. Lett. 2005, 7, 2977-2980.
18. +-C-H⋯ O=C hydrogen bond interactions, see: Cannizzaro, C. E.; Houk, K. N. J. Am. Chem. Soc. 2002, 124, 7163-7169.
19. Calculated using the CPCM solvation model, (a) Barone, B.; Cossi, M. J. Phys. Chem. 1998, 102, 1995-2001.
20. (b) Barone, B.; Cossi, M.; Tomasi, J. J. Comput. Chem. 1998, 19, 404-417.
21. An extensive conformation search evaluating both re- and si-imine facial selectivity identified α-TS2 and γ-TS2 as the lowest energy transition state structures for α- and γ-addition.
22. Thermochemical data and coodinates for zwitterionic intermediates 9 and 14 as well as ring closure transition states α-TSS and γ-TS5 can be found in Supporting Information.
23. Redistribution of charge density from nitrogen (Mulliken charge = -0.55) to the sulfone oxygen closest to phosphorous (Mulliken charge = -0.63) via n →σs-oz.ast; donation has a second-order perturbation energy of mixing 9.37 kcal/mol based on NBO analysis.
24. For previous theoretical discussions of anomeric sulfonamide nitrogen lone pair donation into the S-O* bond, see: Lee, P. S.; Du, W.; Boger, D. L.; Jorgensen, W. L. J. Org. Chem. 2004, 69, 5448-5453 and references therein.
25. Experimentally an 83% yield of the α-addition product and 13% yield of a three-component adduct resulting from initial γ-addition is isolated. This product distribution corresponds to a ratio of 84:16.