Journal of the American Chemical Society
Communication
remains to be addressed. When the ortho-positions are blocked,
the expected para-product is obtained (Table 1, entries 15−
17). Most interestingly, selective catalysts for ortho−ortho,
ortho−para, and para−para coupling of 2,3,5-trimethylphenol
have been identified (Table 1, entries 4−6) showing the
versatility of this catalytic aerobic coupling.
At this juncture, the question of cross-coupling different
phenols arose, a very difficult venture since any catalyst must
promote the cross-coupling much faster than either of the
corresponding homo-couplings.2,12,13 Initially, phenols with
only one open coupling site were used limiting the outcome to
three coupling products (Table 2, entries 1−2). Remarkably, a
Cr catalyst affected cross-coupling with high efficiency (75−
85%) with only a 1.2:1 reactant stoichiometry.
(1S10RR022442) and the NSF for X-ray (CHE 0840438).
T.C. thanks the Vietnam Education Foundation for a
fellowship.
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ASSOCIATED CONTENT
* Supporting Information
Experimental procedures and spectral data. This material is
■
S
AUTHOR INFORMATION
Corresponding Author
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the NSF (CHE1213230, CHE0848460) for
financial support. Partial instrumentation support was provided
by the NIH for MS (1S10RR023444) and NMR
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dx.doi.org/10.1021/ja500183z | J. Am. Chem. Soc. 2014, 136, 6782−6785