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Chemical Science
A. Metzger, S. Hug and P. Knochel, Chem. Commun., 2008, 19 Ligand-free nickel does not provide high yields (Table 2,
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entry 7) and excess nickel does not negatively impact
reactions.1a
V. Krasovskaya, A. Krasovskiy and B. H. Lipshutz, Chem.– 20 See ESI,† Scheme S1 and Chart S1–S10 for further selectivity
Asian J., 2011, 6, 1974; (f) V. Krasovskaya, A. Krasovskiy, and optimization details.
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substrates with a prime. For example, 3c and 3c0 are made
from a different disconnection. 3a and 3a0 are made from
differentbenzyl alcohol derivatives.
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M. F. Haddow, J. N. Harvey, J. Nunn, R. A. Okopie and 24 See ref 13c and f for examples of coupling benzyl phosphate
R. F. Sankey, Angew. Chem., Int. Ed., 2012, 51, 5435; (i) esters with arylmetal reagents.
M. L. N. Rao and R. J. Dhanorkar, RSC Adv., 2013, 3, 6794; 25 The relative leaving group ability can be estimated from the
(j) H.-Q. Do, E. R. R. Chandrashekar and G. C. Fu, J. Am.
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S. Zhang and G.-J. Deng, Org. Lett., 2013, 15, 1520; (m)
pKa data available in the literature for MsOH (1.6 in DMSO)
and (PhO)2P(O)OH (3.9 in DMSO). See: (a) F. G. Bordwell and
D. Algrim, J. Org. Chem., 1976, 41, 2507; (b) P. Christ,
¨
A. G. Lindsay, S. S. Vormittag, J.-M. Neudor, A. Berkessel
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M. R. Harris, L. E. Hanna, M. A. Greene, C. E. Moore and 26 For examples of stereoselective or stereospecic coupling of
E. R. Jarvo, J. Am. Chem. Soc., 2013, 135, 3303; (n) Q. Zhou,
H. D. Srinivas, S. Dasgupta and M. P. Watson, J. Am. Chem.
benzylic substrates, see ref 13j, k and m–p, and the
references in the following endnote.
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14 Commercial availability: 6,152 ArCH2OH vs. 2,357
ArCH2NH2 vs. 605 ArCH2Cl vs. 948 ArCH2Br; data from
eMolecules database (eMolecules, Inc.), accessed via
REAXYS (Elsevier, Inc.) on April 21, 2014.
15 For one example of coupling benzyl chloride (2 equiv.) with
an aryl bromide that might not proceed through an
organometallic intermediate, see: M. Amatore and
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28 Diarylethane 8 has been previously synthesized by the
enantiospecic coupling of secondary benzylsilicon and
benzylboron reagents with aryl iodides or aryl triates.
Yields over the two steps were 41–51% with a 34%–83% ee.
See: (a) Y. Hatanaka and T. Hiyama, J. Am. Chem. Soc.,
1990, 112, 7793; (b) D. Imao, B. Glasspoole, V. r. Laberge
and C. Crudden, J. Am. Chem. Soc., 2009, 131, 5024; (c)
B. W. Glasspoole, M. S. Oderinde, B. D. Moore, A. Anto-
Finch and C. M. Crudden, Synthesis, 2013, 45, 1759.
16 A. H. Cherney and S. E. Reisman, J. Am. Chem. Soc., 2014, 29 Further study is needed to better understand reactions of
136, 14365.
secondary benzylic chlorides. For these electrophiles, a co-
catalyst may not be required. In preliminary studies,
reactions run without added Co(Pc) provided similar
results to reactions run with Co(Pc). Unlike reactions with
vinyl bromides (ref. 16), reactions with bis(oxazoline)
ligands provided low yields of racemic material.
17 Co(Pc) reacted with benzyl mesylate to form benzyl radicals,
quantitated as toluene (5, 4%) and bibenzyl (42%). See Table
S1 in the ESI.†
18 Conditions: 1:1 PhI: BnBr, 7 mol% NiBr2$3H2O, 5 mol%
ꢀ
dtbbpy, and 2 equiv. Zn dust in DMA (0.25 M) at 60 C for
10 min. BnBr is consumed, most of the iodobenzene
remains.
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