Journal of the American Chemical Society
Communication
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11124−11127.
(17) For leading references to nickel-catalyzed cross-couplings
wherein C−O (and C−F) bonds are cleaved, see: Rosen, B. M.;
Quasdorf, K. W.; Wilson, D. A.; Zhang, N.; Resmerita, A.-M.; Garg, N.
K.; Percec, V. Chem. Rev. 2011, 111, 1346−1416. Cross-couplings of
aryl chlorides, and especially aryl bromides and iodides, are
commonplace.
(18) For studies of nickel-catalyzed couplings of secondary alkyl
nucleophiles with aryl or alkenyl electrophiles, see: (a) Tamao, K.;
Kiso, Y.; Sumitani, K.; Kumada, M. J. Am. Chem. Soc. 1972, 94, 9268−
9269. (b) Hayashi, T.; Konishi, M.; Kobori, Y.; Kumada, M.; Higuchi,
T.; Hirotsu, K. J. Am. Chem. Soc. 1984, 106, 158−163. (c) Joshi-Pangu,
A.; Ganesh, M.; Biscoe, M. R. Org. Lett. 2011, 13, 1218−1221.
(19) For leading references, see refs 3a and 3b.
(3) For recent examples of reactions of secondary electrophiles (as a
function of their organometallic coupling partner) and leading
references, see the following. (a) Boron: Wilsily, A.; Tramutola, F.;
Owston, N. A.; Fu, G. C. J. Am. Chem. Soc. 2012, 134, 5794−5797.
(b) Zinc: Choi, J.; Fu, G. C. J. Am. Chem. Soc. 2012, 134, 9102−9105.
(c) Magnesium: Lou, S.; Fu, G. C. J. Am. Chem. Soc. 2010, 132,
1264−1266. (d) Silicon: Dai, X.; Strotman, N. A.; Fu, G. C. J. Am.
Chem. Soc. 2008, 130, 3302−3303. (e) Zirconium: Lou, S.; Fu, G. C. J.
Am. Chem. Soc. 2010, 132, 5010−5011. (f) Indium: Caeiro, J.; Sestelo,
J. P.; Sarandeses, L. A. Chem.Eur. J. 2008, 14, 741−746.
(4) For a recent application in the total synthesis of carolacton
(enantioselective Negishi cross-coupling of a racemic allylic chloride),
see: Schmidt, T.; Kirschning, A. Angew. Chem., Int. Ed. 2012, 51,
1063−1066.
(20) For a report of primary-to-secondary isomerization (2%) in a
palladium-catalyzed Negishi reaction, see: Han, C.; Buchwald, S. L. J.
Am. Chem. Soc. 2009, 131, 7532−7533.
(21) For early mechanistic studies of nickel-catalyzed Negishi
reactions of unactivated alkyl electrophiles, see: (a) Jones, G. D.;
Martin, J. L.; McFarland, C.; Allen, O. R.; Hall, R. E.; Haley, A. D.;
Brandon, R. J.; Konovalova, T.; Desrochers, P. J.; Pulay, P.; Vicic, D. A.
J. Am. Chem. Soc. 2006, 128, 13175−13183. (b) Phapale, V. B.;
(5) For an example of a cobalt-catalyzed asymmetric coupling of a
tertiary alkyl bromide with an allylmagnesium reagent that proceeds in
22% ee and 49% yield, see: Tsuji, T.; Yorimitsu, H.; Oshima, K. Angew.
Chem., Int. Ed. 2002, 41, 4137−4139.
(6) Zultanski, S. L.; Fu, G. C. J. Am. Chem. Soc. 2011, 133, 15362−
15364. A single example of an asymmetric secondary−secondary
cross-coupling is described, specifically, a Suzuki reaction of an
unactivated alkyl bromide with cyclopropyl-(9-BBN) that proceeds in
84% ee and 70% yield.
́
Bunuel, E.; García-Iglesias, M.; Cardenas, D. J. Angew. Chem., Int. Ed.
̃
2007, 46, 8790−8795. (c) Lin, X.; Phillips, D. L. J. Org. Chem. 2008,
73, 3680−3688.
(22) Only one report of asymmetric Negishi reactions of alkyl
electrophiles has employed a bidentate, rather than a tridentate, ligand
(ref 3b). All else being equal, β-hydride elimination may be more facile
in the case of lower-coordinate nickel complexes.
(7) For a review, see: Negishi, E.-i.; Hu, Q.; Huang, Z.; Wang, G.;
Yin, N. In The Chemistry of Organozinc Compounds; Rappoport, Z.,
Marek, I., Eds.; Wiley: New York, 2006; Chapter 11.
(23) For alkyl−alkyl cross-couplings, if transmetalation precedes
oxidative addition (e.g., Figure 1), there may be a greater propensity
for isomerization of the alkyl group derived from the nucleophile,
relative to isomerization of the alkyl group derived from the
electrophile and relative to mechanisms wherein oxidative addition
occurs first.
(24) The data in eq 6 also suggest that reversible homolysis of the
Ni−cyclopentyl bond is probably not occurring during the course of
the cross-coupling.
(8) Arp, F. O.; Fu, G. C. J. Am. Chem. Soc. 2005, 127, 10482−10483.
(9) For applications of pybox ligands, see: (a) Fischer, C.; Fu, G. C. J.
Am. Chem. Soc. 2005, 127, 4594−4595. (b) Ref 8. (c) Son, S.; Fu, G.
C. J. Am. Chem. Soc. 2008, 130, 2756−2757. (d) Smith, S. W.; Fu, G.
C. J. Am. Chem. Soc. 2008, 130, 12645−12647. (e) Lundin, P. M.;
Esquivias, J.; Fu, G. C. Angew. Chem., Int. Ed. 2009, 48, 154−156.
(f) Oelke, A. J.; Sun, J.; Fu, G. C. J. Am. Chem. Soc. 2012, 134, 2966−
2969.
(10) For an application of a bis(oxazoline), see ref 3b.
(11) (a) For initial reports of the use of chiral pyridine−oxazoline
ligands in asymmetric catalysis, see: Brunner, H.; Obermann, U. Chem.
Ber. 1989, 122, 499−507. Nishiyama, H.; Sakaguchi, H.; Nakamura,
T.; Horihata, M.; Kondo, M.; Itoh, K. Organometallics 1989, 7, 846−
848. (b) For a recent application of a chiral pyridine−oxazoline ligand
in palladium-catalyzed conjugate additions of arylboronic acids to
cyclic enones, see: Kikushima, K.; Holder, J. C.; Gatti, M.; Stoltz, B. M.
J. Am. Chem. Soc. 2011, 133, 6902−6905. (c) For a review of
applications of oxazoline-containing ligands in asymmetric catalysis,
see: Hargaden, G. C.; Guiry, P. J. Chem. Rev. 2009, 109, 2505−2550.
(12) To the best of our knowledge, isoquinoline−oxazoline ligand 1
has not previously been reported. It is prepared in one step from
isoquinoline-1-carbonitrile and tert-leucinol.
(13) (a) For a previous report of the beneficial effect of a halide salt
on an enantioselective cross-coupling of an alkyl electrophile, see ref
9c. (b) Possible explanations for the beneficial effect of the halide salt
include in situ formation of a benzylic iodide and the generation of
more reactive zincate complexes. For a recent discussion and leading
references regarding zincate adducts, see: McCann, L. C.; Hunter, H.
N.; Clyburne, J. A. C.; Organ, M. G. Angew. Chem., Int. Ed. 2012, 51,
7024−7027.
(14) Under our standard conditions, a benzylic chloride was not a
suitable cross-coupling partner (high ee, low yield), and hindered
electrophiles (e.g., R1 = isopropyl in Table 2) couple in significantly
lower yield.
(15) The use of CsI rather than MgI2 led to slightly diminished ee
and yield.
(16) Under our standard conditions, cyclohexylzinc iodide cross-
couples with 1-bromo-1-phenylpropane in 54% yield and <5% ee;
however, by further optimizing this process, we have been able to
generate the desired product in up to 61% ee.
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dx.doi.org/10.1021/ja308460z | J. Am. Chem. Soc. 2012, 134, 17003−17006