Organic Letters
Letter
Scheme 2. Scope of Non-ortho-substituted Aryl N-Heteroaryl
Experimental details and characterization data (PDF)
Ketones
AUTHOR INFORMATION
Corresponding Author
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ORCID
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We are grateful for financial support from the National Natural
Science Foundation of China (21202092) and for a Startup
Foundation from the China Three Gorges University
(KJ2012B080, KJ2014H008).
REFERENCES
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pyridyl ketones 12 and 13 were also opposite to those of their
N-oxides, and the reduction of 12 and 13 through method B
afforded the corresponding alcohols in S configuration with
99.8% and 99.6% ee. By contrast, the reduction of electron-
poor aryl 2-pyridyl ketone 14 through methods A and B
afforded the alcohols in the same configuration with 53.4% and
99.9% ee, respectively.
Based on the experimental results, as well as the putative
outer sphere mechanism for the reduction of simple aryl
ketones developed by Noyori,21 we propose that the
enantioselectivity originates from CH/π interaction between
the edge of an η6-arene ligand and the face of an aromatic ring.
In the case of aryl N-heteroaryl ketones, the (R)-enantiomers
were formed, possibly via a transition state by avoiding edge-to-
face interaction with the electron-deficient N-heteroaryl ring, as
depicted in Figure 3a.22 As for the N-oxide ketones, the edge-
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Figure 3. Proposed preferable transition states formed by edge-to-face
interaction between the ligand and substrate.
to-face interaction between the η6-arene ligand and relatively
electron-rich N-oxide pyridine ring is favorable, affording the
alcohols with the S configuration.
In summary, we have developed an efficient asymmetric
transfer hydrogenation of aryl N-heteroaryl ketones with a
commercially available bifunctional oxo-tethered ruthenium
complex in an aqueous solution. Further studies on the
asymmetric transfer hydrogenation of non-ortho-substituted
aryl N-heteroaryl ketones as well as the reaction mechanism are
ongoing in our laboratory.
ASSOCIATED CONTENT
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