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(c) Tra¨ff, A.; Boga´r, K.; Warner, M.; Ba¨ckvall, J.-E. Org. Lett. 2008, 10,
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(2) (a) Leijondahl, K.; Bore´n, L.; Braun, R.; Ba¨ckvall, J.-E. Org. Lett. 2008,
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lead to racemization of the alcohol (step iii), the double bond can
coordinate to ruthenium (step iV). Complexes 10a-b would then
be formed via migration of the alkoxy moiety to the CO ligand
(migratory insertion, step V), which would explain the easy
formation of the large ring (10a-b).17 An alternative pathway for
formation of 10a-b would be migration of the alkoxy group to
CO in 11 (step Vi) followed by coordination of the double bond
(step Vii).
(4) (a) Abbel, R.; Abdur-Rashid, K.; Faatz, M.; Hadzovic, A.; Lough, A. J.;
Morris, R. H. J. Am. Chem. Soc. 2005, 127, 1870–1882. (b) Casey, C. P.;
Clark, T. B.; Guzei, I. A. J. Am. Chem. Soc. 2007, 129, 11821–11827. (c)
Hamilton, R. J.; Bergens, S. H. J. Am. Chem. Soc. 2008, 130, 11979–
11987.
Scheme 3. Possible Routes for the Formation of 10a-b
(5) Mart´ın-Matute, B.; Åberg, J. B.; Edin, M.; Ba¨ckvall, J.-E. Chem.sEur. J.
2007, 13, 6063–6072.
(6) Åberg, J. B.; Nyhle´n, J.; Mart´ın-Matute, B.; Privalov, T.; Ba¨ckvall, J.-E.
J. Am. Chem. Soc. 2009, 131, 9500–9501.
(7) Nyhle´n, J.; Privalov, T.; Ba¨ckvall, J.-E. Chem.sEur. J. 2009, 15, 5220–
5229.
(8) Only two of the four possible diastereoisomers were observed [there are
three stereogenic centers: the ruthenium, the R-carbon of the alcohol (C2),
and one of the coordinated carbons of the alkene (C5)].
(9) McWilliams, K. M.; Angelici, R. J. Organometallics 2007, 26, 5111–5118.
(10) Alvarez, P.; Lastra, E.; Gimeno, J.; Brana, P.; Sordo, J. A.; Gomez, J.;
Falvello, L. R.; Bassetti, M. Organometallics 2004, 23, 2956–2966.
(11) The assignments of the protons were made by conventional 2D NMR
experiments (see the Supporting Information for further details).
(12) Selg, P.; Brintzinger, H. H.; Andersen, R. A.; Horva´th, I. T. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 791–793.
(13) A heteronuclear multiple bond correlation (HMBC) spectrum shows cross-
peaks for long-range couplings between protons and carbons.
(14) (a) Dutta, B.; Scopelliti, R.; Severin, K. Organometallics 2008, 27, 423–
429. (b) Suzuki, H.; Omori, H.; Mor-oka, Y. J. Organomet. Chem. 1987,
327, C47–C50. (c) Taube, D. J.; Rokicki, A.; Anstock, M.; Ford, P. C.
Inorg. Chem. 1987, 26, 526–530.
(15) (a) Taube, D. J.; Rokicki, A.; Anstock, M.; Ford, P. C. Inorg. Chem. 1987,
26, 526–530. (b) Trautman, R. J.; Gross, D. C.; Ford, P. C. J. Am. Chem.
Soc. 1985, 107, 2355–2362.
(16) Other mechanisms for racemization are also possible. These include a formyl
intermediate (I), an acyloxy intermediate (II), and a hydroxyl carbene
intermediate (III):
The rate of racemization would be slow because ruthenium is
held as inactive 10a-b. In Scheme 3 we have assumed that the
racemization occurs via ꢀ-hydride elimination. However, other
racemization mechanisms are also possible, such as those involving
CO participation.16 In these alternative mechanisms, the rate of
racemization would also be slowed by the formation of 10a-b.
In conclusion, we have used 1H and 13C NMR spectroscopy and
in situ FT-IR measurements to characterize two diastereomers (10a
and 10b)18 of an alkoxycarbonyl complex having a double bond
coordinated to ruthenium. IR peaks were observed at 1982 cm-1
(CO) and 1644 (acyl) cm-1. These studies have provided further
insight into the mechanism of the highly efficient racemization
catalyst 1.
Acknowledgment. The Swedish Research Council, the Berze-
lius Center EXSELENT, and the K. & A. Wallenberg Foundation
are gratefully acknowledged for financial support.
(17) The easy formation of a seven-membered ring from a six-membered ring
via 1,2-migration is known in a number of rearrangements, e.g., the
Beckman rearrangement and the Baeyer-Villiger oxidation.
Supporting Information Available: Experimental procedures and
characterization data for all new compounds. This material is available
(18) Only two of the four possible diatereomers were observed. Density
functional theory calculations indicate that the change in the configuration
at C5 relative to the configuration at Ru leads a significant energy change.
This means that for a given Ru configuration, it is energetically favorable
to coordinate one face of the alkene, whereas coordination of the other
face is very unfavored. The two diastereoisomers observed must therefore
have the same or opposite absolute configuration at C2 and C5 (2R,5R-
2S,5S, or 2R,5S-2S,5R) (Nyhle´n, J., unpublished results).
References
(1) (a) Mart´ın-Matute, B.; Edin, M.; Boga´r, K.; Ba¨ckvall, J.-E. Angew. Chem.,
Int. Ed. 2004, 43, 6535–6539. (b) Mart´ın-Matute, B.; Edin, M.; Boga´r, K.;
Kaynak, F. B.; Ba¨ckvall, J.-E. J. Am. Chem. Soc. 2005, 127, 8817–8825.
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