Stereocontrolled coupling between aldehydes and conjugated alkenals mediated by TiIII/H2O

Organic Letters

Volumn 8, Issue 24, 2006, Pages 5433-5436

  Estévez, Rosa E ^a   Oller Lopez, Juan L ^a   Robles, Rafael ^a   Melgarejo, Concepción R ^a   Gansäuer, Andreas ^b   Cuerva, Juan M ^a   Oltra, J Enrique ^a  

^a UNIVERSITY OF GRANADA   (Spain)

^b UNIVERSITY OF BONN   (Germany)

Author keywords

[No Author keywords available]

Indexed keywords

EID: 33845970893     PISSN: 15237060     EISSN: None     Source Type: Journal    
DOI: 10.1021/ol0620390     Document Type: Article

References (36)

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3. For a review, see: Molander, G. A. In Radicals in Organic Synthesis; Renaud, P., Sibi, M. P., Eds.; Wiley-VCH: Weinheim: 2001; Vol. 1, pp 165-174.
4. 2-mediated intramolecular addition of aldehydes to conjugated alkenones: (a) Sato, A.; Masuda, T.; Arimoto, H.; Uemura, D. Org. Biomol. Chem. 2005, 3, 2231-2233.
5. (b) Nguyen, T. C.; Lee, D. Tetrahedron Lett. 2002, 43, 4033-4036.
6. We have also found two reports dealing with the electrohydrodimerization of α,β-unsaturated aldehydes: (c) Barba, F.; de la Fuente, J. L.; Galakhov, M. Tetrahedron, 1997, 53, 5831-5838.
7. (d) Johnston, J. C.; Faulkner, J. D.; Mandell, L.; Day, R. A., Jr. J. Org. Chem. 1976, 41, 2611-2614.
8. 2TiCl.
9. Brintzinger's complexes dichloro[(R,R)-ethylenebis-(4,5,6,7-tetrahydro-1- indenyl)]-titanium(IV) and its enantiomer can be bought from commercial sources or prepared by the resolution of (rac)-ethylenebis-(tetrahydroindenyl)- titanium derivatives; see: Chin, B.; Buchwald, S. L. J. Org. Chem. 1996, 61, 5650-5651.
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18. Oller-López, J. L.; Campaña, A. G.; Cuerva, J. M.; Oltra, J. E. Synthesis 2005, 2619-2622.
19. Lactol 2 was accompanied by a trace of its 4R*, 5R* stereoisomer.
20. Lactol 5 was accompanied by a minor amount (9%) of the pinacol coupling product (dl/meso, 3/2) and a trace of its 4R*, 5S* stereoisomer.
21. We utilized NOE studies as well as oxidation to the corresponding γ-lactones to confirm the stereochemistry of γ-lactols described in Table 1. For experimental details see Supporting Information.
22. Connolly, J. D.; Hill, R. A. Dictionary of Terpenoids; Chapman & Hall: London, 1991.
23. 2O-promoted reduction of the excess (1 equiv) of 6 or 7 employed for these syntheses.
24. Cuerva, J. M.; Campaña, A. G.; Justicia, J.; Rosales, A.; Oller-López, J. L.; Robles, R.; Cárdenas, D.; Buñuel, E.; Oltra, J. E. Angew. Chem., Int. Ed. 2006, 45, 5522-5526.
25. In contrast, the pinacol-type coupling (head-to-head) would correspond to a 5-endo-dig cyclization disfavored by Baldwin's rules, thus explaining the regioselectivity toward head-to-tail coupling products observed. For Baldwin's rules, see: (a) Clayden, J.; Greeves, N.; Warren, S.; Wothers, P. Organic Chemistry; Oxford University Press: Oxford, 2001; pp 1140-1144.
26. (b) Baldwin, J. E.; Lusch, M. J. Tetrahedron 1982, 38, 2939-2947.
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32. Twenty-five percent dialdehyde 29 was recovered unchanged.
33. Besides 27a and 27b, a trace of a third trans-fused menthane lactone, the 3R*,3aR*,6R*, 7aS* diastereomer, was detected. GC-MS analysis indicated that these three lactones constituted more than a 96% of the mixture.
34. Gansäuer, A.; Bluhm, H.; Pierobon, M. J. Am. Chem. Soc. 1998, 120, 12849-12859.
35. Enantiomeric excess (ee) was determined on the acetyl derivative of (+)-17 with the aid of chiral lanthanide NMR shift reagents; see: Sweeting, L. M.; Crans, D. C.; Whitesides, G. M. J. Org. Chem. 1987, 52, 2273-2276.
36. Rosales, A.; Oller-López, J. L.; Justicia, J.; Gansäuer, A.; Oltra, J. E.; Cuerva, J. M. Chem. Commun. 2004, 2628-2629.