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efficiently. The coupling of terminal alkylalkynes and internal
arylalkynes only gave trace amounts of desired products. While a
wide range of nonactivated alkyl halides were suitable substrates,
activated alkyl halides, such as benzylic/allylic bromides and α-
bromoketones, did not react to give the desired Z-olefins but
underwent reductive dimerization under the catalytic conditions.
Thus, the current method is not yet as general as Wittig reaction,
cross-coupling, or semihydrogenation. However, the high Z-
selectivity and the simple and practical conditions provided by
this method make it a novel and valuable approach for the
synthesis of Z-β-alkylstyrenes.
(12) For recent works on Fe-catalyzed reductive coupling with CC
double bonds, see: (a) Greenhalgh, M. D.; Thomas, S. P. ChemCatChem.
2014, 6, 1520−1522. (b) Jones, A. S.; Paliga, J. F.; Greenhalgh, M. D.;
Quibell, J. M.; Steven, A.; Thomas, S. P. Org. Lett. 2014, 16, 5964−4967.
(c) Lo, J. C.; Gui, J.; Yabe, Y.; Pan, C.-M.; Baran, P. S. Nature 2014, 516,
343−348.
(13) Fe-catalyzed reductive coupling between ArBr and alkenyl
bromide using Mg as reductant has been reported, see: Czaplik, W. M.;
Mayer, M.; von Wangelin, A. J. ChemCatChem 2011, 3, 135−138.
ASSOCIATED CONTENT
* Supporting Information
■
S
Experimental and spectral data. This material is available free of
(14) (a) Furstner, A.; Martin, R. Chem. Lett. 2005, 34, 624−629.
̈
(b) Sherry, B. D.; Furstner, A. Acc. Chem. Res. 2008, 41, 1500−1511.
̈
(15) (a) Furstner, A.; Martin, R.; Krause, H.; Seidel, G.; Goddard, R.;
Lehmann, C. W. J. Am. Chem. Soc. 2008, 130, 8773−8787. (b) Adams, C.
J.; Bedford, R. B.; Carter, E.; Gower, N. J.; Haddow, M. F.; Harvey, J. N.;
̈
AUTHOR INFORMATION
Corresponding Author
■
́
Huwe, M.; Cartes, M. A.; Mansell, S. M.; Mendoza, C.; Murphy, D. M.;
Neeve, E. C.; Nunn, J. J. Am. Chem. Soc. 2012, 134, 10333−10336.
(16) For alkyl halides, reduction and homocoupling occurred to some
degree. For terminal alkynes, no reduction or dimerization was
observed. The conversion of alkynes was between 80 and 100%. The
isolation and purification of products were straightforward.
(17) The low to moderate yields for arylalkynes bearing carbonyl
groups might be partially due to pinacol coupling reaction.
(18) The modified protocol is applicable to the coupling of secondary
and tertiary alkyl halides as well, having similar efficiency as the
unmodified protocol.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work is supported by a European Research Council (ERC)
starting grant (no. 257096) and by the Swiss State Secretariat of
Education, Research, and Innovation (C13.0038).
(19) Sun, C.-L.; Krause, H.; Furstner, A. Adv. Synth. Catal. 2014, 356,
1281−1291.
(20) Tron, G. C.; Pirali, T.; Sorba, G.; Pagliai, F.; Busacca, S.;
Genazzani, A. A. J. Med. Chem. 2006, 49, 3033−3044.
(21) Nagaoka, T.; Banskota, A. H.; Tezuka, Y.; Saiki, I.; Kadota, S.
Bioorg. Med. Chem. 2002, 10, 3351−3359.
(22) The coupling of caffeic acid 6-iodohexyl ester would be a more
direct method to prepare the target compound. However, the enoate
and phonol groups might not be compatible. Moreover, an excess of
alkyl halide is required in this step, which is unfavorable for using a highly
functionalized alkyl halide such as caffeic acid 6-iodohexyl ester.
(23) Buckle, D. R. (Beecham Group p.l.c., England) Novel
Compounds. U.S. Patent US4713486, December 15, 1987.
(24) Jiao, X.-Y.; Bentrude, W. G. J. Am. Chem. Soc. 1999, 121, 6088−
6089.
(25) The pKa of acidic C(sp)-H by phenylacetylene and water in
(26) Huo, S. Org. Lett. 2003, 5, 423−425.
(27) The reduction of FeBr2 to Fe(0) particle could not be ruled out;
see ref 8c.
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