Journal of the American Chemical Society
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other chiral compounds without loss of enantiomeric purity
(Scheme 4). Cross-coupling of (R)-3dc with excess Grignard
reagents RMgBr (R = Me, Ph) proceeded in the presence of a
Ni/dppp catalyst in refluxing benzene to give the corre-
sponding disubstitution products 8a and 8b in high yields.22,23
Selective monophenylation of (R)-3dc producing 9 was found
to be catalyzed well by a rhodium/Ph-bod complex in the
presence of excess Ph-bod ligand in toluene/H2O solvent sys-
tem.24 The monophenylation is assumed to proceed through
phenylrhodation/β-F elimination mechanism25 with G as an
intermediate. Interestingly, the phenylation did not take place
at all with cod or phosphorus ligands (PPh3, dppp), while it
was promoted by Ph-bod and Fc-tfb ligands. Scheme 4 also
shows hydrogenation of the difluoroethenyl group into difluo-
roethyl group and deprotection of phthalimino group in (R)-
3ba into amino group without loss of % ee.
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In summary, we have developed a new type of catalytic
asymmetric reaction where 1-(trifluoromethyl)alkenes
(CF3CH=CHR) are converted into chiral 1,1-difluoroalkenes
(CF2=CHC*HArR) with high enantioselectivity (≥95% ee) by
the reaction with arylboroxines (ArBO)3 in the presence of a
chiral diene-rhodium catalyst. The CF3 group plays key roles
in activating the alkene substrates towards arylrhodation and
in carrying the catalytic cycle by β-fluoride elimination of a
β,β,β-trifluoroalkylrhodium intermediate as a key step.
ASSOCIATED CONTENT
Supporting Information. Experimental procedures, compound
characterization data, and crystallographic data (CIF). This mate-
rial is available free of charge via the Internet at
AUTHOR INFORMATION
Corresponding Author
ACKNOWLEDGMENT
We thank Nanyang Technological University for sup-
porting this research.
(17) (a) Otomaru, Y.; Okamoto, K.; Shintani, R.; Hayashi, T. J. Org.
Chem. 2005, 70, 2503. (b) Abele, S.; Inauen, R.; Spielvogel, D.;
Moessner, C. J. Org. Chem. 2012, 77, 4765.
(18) Dou, X.; Huang, Y.; Hayashi, T. Angew. Chem., Int. Ed. 2016,
55, 1133.
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