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glass syringes with a metallic needle and metallic spatulas that
we usually use. For details, see the Supporting Information.
[11] 2-Naphthyl triflate was much less reactive than the correspond-
ing bromide (2’a) and gave 3aa in only 4% yield (4% conv.) in
the reaction with 1a under the conditions of entry 14 in Table 2.
Aryl triflates are usually more reactive than aryl bromides under
transition-metal catalysis.
[4] For the coupling with alkenyl halides: E. Shirakawa, R. Watabe,
[5] The transition-metal-free cross-coupling reaction of allyl halides
with aryl- and alkenylboronic acids has been reported, for which
a
nonradical mechanism is proposed; a) A. Scrivanti, V.
[12] ZnCl2 (anhydrous powder, ꢀ 99.995% trace metals basis,
Aldrich Co., product number 429430) was used. Magnesium
turning (99.95% purity trace metals basis, Aldrich Co., product
number 403148) was used for the preparation of the Grignard
reagents in Scheme 1. For analysis of the magnesium turning, see
footnote 9 of Ref. [3a].
[13] MgX2 (X = halogen) generated upon transmetalation might
alter the structure of the zincate derived from PhZnX and
LiCl and thus affect its reactivity. For a report on the effect of the
method used to prepare the arylzinc halides on the efficiency of
the reaction, see: L. Jin, C. Liu, J. Liu, F. Hu, Y. Lan, A. S.
Batsanov, J. A. K. Howard, T. B. Marder, A. Lei, J. Am. Chem.
[14] Although it is unclear how diglyme affects the reaction,
a possible explanation is that the magnesium halides produced
upon transmetalation have a negative effect that is negated by
complexation of the salt with diglyme. For complexation of
magnesium halides with diglyme, see: a) Y. Saheki, K. Sasada, N.
b) N. Metzler, H. Noeth, M. Schmidt, A. Z. Treitl, Z. Natur-
forsch. B 1994, 49, 1448 – 1451.
[7] The coupling of PhMgBr (1.5 equiv) with 2a in toluene in the
presence of THF (6 equiv) at 1108C for 24 h gave 3aa in 96%
yield. See Ref. [3a].
[8] Formation of lithium organozincates such as Li+[RZnXCl]À
upon mixing RZnX (R = alkyl or aryl) with LiCl has been
confirmed; a) J. E. Fleckenstein, K. Koszinowski, Organometal-
enhancement of the reactivities of organozinc reagents by
addition of LiCl, see: b) A. Krasovskiy, V. Malakhov, A.
5377; d) N. Boudet, S. Sase, P. Sinha, C.-Y. Liu, A. Krasovskiy, P.
1110; f) H. Ochiai, M. Jang, K. Hirano, H. Yorimitsu, K. Oshima,
ꢃlvarez, A. R. Kennedy, M. D. McCall, L. Russo, E. Hevia,
[15] Diglyme/THF/TMU (5:4:1) was a better solvent system than
diglyme/THF (3:2) in the reactions shown in Scheme 1 except
for that of 1a with 2b.
[16] For an example of utilization of a radical anion of an arene,
sodium naphthalenide, as a single-electron donor in the SRN1
reaction, see: G. A. Russell, R. K. Norris, E. J. Panek, J. Am.
[17] For examples of utilization of SmI2 as a single-electron donor in
the SRN1 reaction, see: a) M. A. Nazareno, R. A. Rossi, Tetrahe-
[18] In our previous report (Ref. [3a]), the addition of LDBB to
a mixture of PhMgBr and 2’a accelerated the reaction. In
contrast, addition in this sequence for 1a and 2’a gave no
acceleration; only 3% or < 1% yield of 3aa was obtained with
LDBB and SmI2, respectively. It is unclear why the addition of
these single-electron donors in the presence of 1a did not work.
In the latter case, SmI2 could be converted into organometallic
species such as Ph2Sm, which may negatively affect the reaction
system.
[9] Zinc powder (99.995% trace metals basis, Aldrich Co., product
number 324930) was used for the preparation of arylzinc
reagents. Inductively coupled plasma atomic emission spectros-
copy (ICP-AES) analysis of the zinc powder showed that the
content of Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Ir, Pt, and Au are less
than 5 ppm (under the detection limit). For details of the ICP-
AES analysis, see the Supporting Information. LiCl (ꢀ 99.99%
trace metals basis, Aldrich Co., product number 203637) was
used as an additive. The reaction of 1a with 2a under the
conditions of entry 4 in Table 1 using a different lot of zinc
powder (99.9% purity, Wako Pure Chemical Industries, product
number 262-01581) or LiCl (99% purity, Wako Pure Chemical
Industries, product number 123-01162) gave essentially the same
result: Zn (Aldrich) and LiCl (Wako), > 99% conv. of 2a, 91%
yield of 3aa, 2% yield of 4, 3% yield of 5; Zn (Wako) and LiCl
(Aldrich), > 99% conv. of 2a, 91% yield of 3aa, 1% yield of 4,
2% yield of 5. It is impossible to completely eliminate the
possibility that small amounts of transition-metal impurities
show some positive effect. But even in that case, they are
considered to be involved in the SET mechanism described
below.
[19] The lifetime of [Ar–X]CÀ is reported to be too short to react with
some substrates owing to fast fragmentation into ArC and XÀ.
However, only data for the reaction in polar solvents such as N-
methylpyrrolidone and N,N-dimethylformamide are available.
For recent examples, see: a) C. Costentin, M. Robert, J.-M.
Takeda, P. V. Poliakov, A. R. Cook, J. R. Miller, J. Am. Chem.
[10] We asked Dr. Yoshiaki Nakao (Graduate School of Engineering,
Kyoto University) to repeat the reaction and he confirmed that
the reaction of PhZnI (1a: prepared by him from Ph–I and Zn)
with ethyl p-iodobenzoate (2b) under the conditions of entry 2
of Table 2 gave 3ab in 85% yield. This result, in conjunction with
the result that the coupling is insensitive to the lot of the reagents
used (Zn and LiCl) as shown in Ref. [9], shows that this method
is reproducible. In addition, 3aa and 3ab were obtained in
similar yields (92% and 88%, respectively) under the conditions
of entries 1 and 2 in Table 2 by using pippeters equipped with
a polypropylene chip and Teflon-coated spatulas instead of the
[20] For example, 0.008 mmol of Ph–Ph was detected by GC in the
reaction of PhZnI (1a: 0.30 mmol) with Np–I (2a: 0.20 mmol;
Table 1, entry 4).
[21] The o-homoallylphenyl radical is known to readily cyclize (kc =
5 ꢄ 108 sÀ1 at 508C): a) A. N. Abeywickrema, A. L. J. Beckwith, J.
an intermediate, it must undergo cyclization at least in part. For
a detailed discussion, see Equation (4) of Ref. [3b] and its
explanatory sentences.
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Angew. Chem. Int. Ed. 2014, 53, 521 –525