Journal of the American Chemical Society
Communication
Scheme 2. Catalytic Mechanism for Ruthenium-Catalyzed Crotylation via Butadiene Hydrohydroxyalkylation
ray diffraction analysis (Figure 2). As anticipated, the phosphate
counterion exists in a trans-relationship with respect to the
carbonyl ligand.10 On the basis of the connectivity revealed in
the crystal structure and the observed stereoselectivities, a
preliminary stereochemical model was formulated and recon-
ciled with the indicated catalytic mechanism (Scheme 2). The
unusual syn-diastereoselectivity may arise as a consequence of
kinetically preferred hydrometalation of the s-cis conformer of
butadiene to furnish the anti-π-crotylruthenium isomer.11 It is
postulated that the steric demand of the TADDOL-based
phosphate counterion retards the rate of isomerization to the
syn-π-crotylruthenium isomer, which would mandate the
intervention of an even more sterically congested secondary
σ-crotylruthenium species. In this way, the kinetic stereo-
selectivity of the hydrometalation event is preserved, and
carbonyl addition occurs by way of the (Z)-σ-crotylruthenium
haptomer via a closed Zimmerman−Traxler-type transition
structure12 to furnish the syn diastereomer.
In summary, we have reported the chiral-anion-dependent
inversion of diastereo- and enantioselectivity in butadiene
hydrohydroxyalkylation to form products of carbonyl syn-
crotylation as well as the first X-ray crystal structure of a
ruthenium complex modified by a chiral phosphate counterion.
These studies have provided important insight into the
structural and interactional features of the catalyst, which
should accelerate the design of improved second-generation
protocols. More broadly, the merged redox-construction events
described herein minimize the degree of separation between
reagent and feedstock and represent a departure from
premetalated reagents in carbonyl addition, a cornerstone of
synthetic organic chemistry.
ACKNOWLEDGMENTS
■
The Robert A. Welch Foundation (F-0038) and the NIH
NIGMS (R01-GM069445) are acknowledged for partial
support of this research.
REFERENCES
■
(1) For recent reviews of C−C bond-forming hydrogenation and
transfer hydrogenation, see: (a) Bower, J. F.; Krische, M. J. Top.
Organomet. Chem. 2011, 43, 107. (b) Hassan, A.; Krische, M. J. Org.
Process Res. Dev. 2011, 15, 1236. (c) Moran, J.; Krische, M. J. Pure
Appl. Chem. 2012, 84, 1729.
(2) For iridium-catalyzed carbonyl crotylation from the alcohol
oxidation level employing α-methyl allyl acetate as the crotyl donor,
see: (a) Kim, I. S.; Han, S. B.; Krische, M. J. J. Am. Chem. Soc. 2009,
131, 2514. (b) Gao, X.; Townsend, I. A.; Krische, M. J. J. Org. Chem.
2011, 76, 2350. (c) Gao, X.; Han, H.; Krische, M. J. J. Am. Chem. Soc.
2011, 133, 12795.
(3) For selected reviews of enantioselective carbonyl allylation and
crotylation, see: (a) Yamamoto, Y.; Asao, N. Chem. Rev. 1993, 93,
2207. (b) Ramachandran, P. V. Aldrichimica Acta 2002, 35, 23.
(c) Kennedy, J. W. J.; Hall, D. G. Angew. Chem., Int. Ed. 2003, 42,
4732. (d) Denmark, S. E.; Fu, J. Chem. Rev. 2003, 103, 2763. (e) Yu,
C.-M.; Youn, J.; Jung, H.-K. Bull. Korean Chem. Soc. 2006, 27, 463.
(f) Marek, I.; Sklute, G. Chem. Commun. 2007, 1683. (g) Hall, D. G.
Synlett 2007, 1644. (h) Li, J.; Menche, D. Synthesis 2009, 2293.
(i) Leighton, J. L. Aldrichimica Acta 2010, 43, 3. (j) Yus, M.; Gonzal
Gomez, J. C.; Foubelo, F. Chem. Rev. 2011, 111, 7774.
́
ez-
́
(4) For iridium- and ruthenium-catalyzed hydrohydroxyalkylations of
butadiene to form products of crotylation, see: (a) Shibahara, F.;
Bower, J. F.; Krische, M. J. J. Am. Chem. Soc. 2008, 130, 6338.
(b) Zbieg, J. R.; Fukuzumi, T.; Krische, M. J. Adv. Synth. Catal. 2010,
352, 2416. (c) Zbieg, J. R.; Moran, J.; Krische, M. J. J. Am. Chem. Soc.
2011, 133, 10582. (d) Zbieg, J. R.; Yamaguchi, E.; McInturff, E. L.;
Krische, M. J. Science 2012, 336, 324.
(5) For selected reviews of chiral phosphate counterions in metal
catalysis, see: (a) Shao, Z.; Zhang, H. Chem. Soc. Rev. 2009, 38, 2745.
(b) Zhong, C.; Shi, X. Eur. J. Org. Chem. 2010, 2999. (c) Rueping, M.;
Koenigs, R. M.; Atodiresei, I. Chem.Eur. J. 2010, 16, 9350.
(d) Phipps, R. J.; Hamilton, G. L.; Toste, F. D. Nat. Chem. 2012, 4,
603. (e) Parra, A.; Reboredo, S.; Martin Castro, A. M.; Aleman, J. Org.
Biomol. Chem. 2012, 10, 5001.
ASSOCIATED CONTENT
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S
* Supporting Information
Experimental procedures and spectral data. This material is
(6) For selected examples of the use of chiral phosphate counterions
in metal catalysis, see: (a) Alper, H.; Hamel, N. J. Am. Chem. Soc. 1990,
112, 2803. (b) Komanduri, V.; Krische, M. J. J. Am. Chem. Soc. 2006,
128, 16448. (c) Hamilton, G. L.; Kang, E. J.; Mba, M.; Toste, F. D.
Science 2007, 317, 496. (d) Rueping, M.; Antonchick, A. P.;
Brinkmann, C. Angew. Chem., Int. Ed. 2007, 46, 6903. (e) Mukherjee,
S.; List, B. J. Am. Chem. Soc. 2007, 129, 11336. (f) Liao, S.; List, B.
Angew. Chem., Int. Ed. 2010, 49, 628. (g) Jiang, G.; List, B. Chem.
AUTHOR INFORMATION
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Corresponding Author
Notes
The authors declare no competing financial interest.
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dx.doi.org/10.1021/ja311208a | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX