Theoretical investigation of the rubicordifolin cascade

Organic Letters

Volumn 12, Issue 22, 2010, Pages 5162-5165

  Lumb, Jean Philip ^a,b   Krinsky, Jamin L ^a   Trauner, Dirk ^a,c  

^a UNIVERSITY OF CALIFORNIA   (United States)

^b STANFORD UNIVERSITY   (United States)

^c UNIVERSITY OF MUNICH   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

BIOLOGICAL PRODUCT; FURAN DERIVATIVE; FUROMOLLUGIN; NAPHTHOL DERIVATIVE; PYRONE DERIVATIVE; RUBICORDIFOLIN;

ARTICLE; CATALYSIS; CHEMICAL STRUCTURE; CHEMISTRY; CYCLIZATION; MEDICINAL PLANT; RUBIA; STEREOISOMERISM; SYNTHESIS;

BIOLOGICAL PRODUCTS; CATALYSIS; CYCLIZATION; FURANS; MODELS, MOLECULAR; MOLECULAR STRUCTURE; NAPHTHOLS; PLANTS, MEDICINAL; PYRONES; RUBIA; STEREOISOMERISM;

EID: 78449286725     PISSN: 15237060     EISSN: 15237052     Source Type: Journal    
DOI: 10.1021/ol102157d     Document Type: Article

References (39)

1. For a review of bioactive natural products derived from Rubia see
2. Chauhan, S.; Singh, R. Chem. Biodiversity 2004, 1, 1241
3. Lumb, J. P.; Trauner, D. J. Am. Chem. Soc. 2005, 127, 2870
4. Lumb, J. P.; Choong, K. C.; Trauner, D. J. Am. Chem. Soc. 2008, 130, 9230
5. Despite the absence of products arising from exo- or regioisomeric transition states in the crude reaction mixture, their formation cannot be unequivocally excluded in light of the incomplete mass balance of the reaction.
6. Frisch, M. J., et al. Gaussian 09, Revision A.2, Gaussian, Inc., Wallingford, CT, 2009. Complete citation in the Supporting Information.
7. Zhao, Y.; Truhlar, D. G. Theor. Chem. Acc. 2008, 120, 215
8. Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys. 1980, 72, 650
9. McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639
10. Grimme, S. J. Chem. Phys. 2006, 124 034108
11. Schwabe, T.; Grimme, S. Phys. Chem. Chem. Phys. 2007, 9, 3397
12. Reed, A. E.; Curtiss, L. A.; Weinhold, F. Chem. Rev. 1988, 88, 899
13. For Natural Localized Molecular Orbital (NLMO) analysis see
14. Reed, A. E.; Weinhold, F. J. Chem. Phys. 1985, 83, 1736
15. Hübler, K.; Hunt, P. A.; Maddock, S. M.; Rickard, C. E. F.; Roper, W. R.; Salter, D. M.; Schwerdtfeger, P. Organometallics 1997, 16, 5076
16. For a recent computational analysis of pseudopericyclic cyclizations see
17. Duncan, J. A.; Calkins, D. E. G.; Chavarha, M. J. Am. Chem. Soc. 2008, 130, 6740 and references cited therein
18. Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105, 2999 Only the activation energy is given here because the T.S. energy is not directly comparable with the other (gas-phase) results.
19. Since the reaction mixture was exposed to ambient light, a radical mechanism could account for the room temperature cyclization of 1. For a related, photoinduced cyclization of vinyl quinones see
20. Iwamoto, H.; Takuwa, A.; Hamada, K.; Fujiwara, R. J. Chem. Soc., Perkin Trans. 1 1999, 5, 575
21. A light-induced radical mechanism in the formation of rubicordifolin seems unlikely, however, since the reaction vessel was thoroughly wrapped in aluminum foil prior to thermolysis.
22. Butyric acid is a known impurity of "aged" THF: Coetzee, J. F.; Chang, T.-H. Pure Appl. Chem. 1985, 57, 633 and references therein
23. For a related room temperature, acid mediated cyclization of vinyl- p -quinones see
24. Taing, M.; Moore, H. W. J. Org. Chem. 1996, 61, 329
25. See the Supporting Information for a complete analysis of protonated 1.
26. The dehydration of 2-(benzofuran-2-yl)propan-2-ol mediated by phenylboronic acid was modeled by using a THF PCM solvent correction. The activation energy is 20.5 kcal/mol and the transformation is endothermic by 8.3 kcal/mol. See the Supporting Information for details.
27. Note that the B2PLYP-D value of 8.0 kcal/mol suggests that the M06-2X value of 2 kcal/mol represents a lower limit in the energetic difference between 1 and 11.
28. The corresponding carboxylic acid of 1 has been evaluated as a potential reactive intermediate. See the Supporting Information for a detailed discussion.
29. For a related cyclization/[4 + 2] cycloaddition cascade see the synthesis of torreyanic acid
30. Li, C.; Johnson, R. P.; Porco, J. A. J. Am. Chem. Soc. 2003, 125, 5095
31. 2O
32. Chen, F.; Kina, A.; Hayashi, T. Org. Lett. 2006, 8, 341
33. For a review of boronic acids in catalysis see
34. Ishihara, K.; Yamamoto, H. Eur. J. Org. Chem. 1999, 3, 527
35. See the Supporting Information for the 4 / 5 cycloaddition.
36. For examples of B3LYP acting poorly in modeling dispersion forces see
37. Šponer, J.; Riley, K. E.; Hobza, P. Phys. Chem. Chem. Phys. 2008, 10, 2595
38. Ujaque, G.; Lee, P. S.; Houk, K. N.; Hentemann, M. F.; Danishefsky, S. J. Chem.-Eur. J. 2002, 8, 3423
39. Zhao, Y.; Truhlar, D. G. J. Chem. Theory Comput. 2006, 2, 1009