Chemistry Letters 2000
1011
mixture of 1 (0.5 × 10–2 mmol, 1 mol%) and MgO (0.5 mmol)
was added a solution of benzyl chloride (0.5 mmol) in benzene
(15 mmol) at room temperature. The mixture was stirred for 8
h at 80 ˚C and then filtered through silica gel. The eluent was
concentrated in vacuo, and the crude product was purified by
preparative TLC to afford diphenylmethane.
Thus, it is noted that a new and convenient method for
Friedel–Crafts benzylation reactions of aromatic compounds
with benzyl chloride or mesylate and their substituted deriva-
tives in the presence of a catalytic amount of, a neutral salt, 1
was established. Further, it was found that the turnover of the
present catalyst 1 is improved by the addition of MgO.
Further investigations to develop other synthetic reactions
using catalytic amounts of 1 as well as to clarify the role of the
MgO in this reaction are now in progress.
The present research is partially supported by Grant-in-
Aids for Scientific Research from the Ministry of Education,
Science, Sports and Culture.
References and Notes
1
a) A. G. Massey and A. J. Park, J. Organomet. Chem., 2, 245
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(1970), Vol. 6, p. 149.
2
a) H. Nishida, N. Takada, M. Yoshimura, T. Sonoda, and H.
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3
4
a) B. Rhodes, J. C. W. Chien, and M. D. Rausch,
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Review articles, see: a) G. A. Olah, R. Krishnamurti, and G. K.
Suryaprakash, “Comprehensive Organic Synthesis,” ed. by B.
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3, p. 293. b) C. C. Price, “The Alkylation of Aromatic
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Reactions,” ed. by R. Adams, Wiley, New York (1962), Vol. 3,
p. 1.
5
6
7
Lithium Tetrakis(pentafluorophenyl)borate–Ethyl Ether
Complex was purchased from Tokyo Chemical Industry Co.,
Ltd. and was stirred under 0.5 mmHg at 60 ˚C for 3 h before use
1
in the Friedel–Crafts reaction. By H NMR measurement, it
was determined that the above pretreated lithium tetrakis(penta-
fluorophenyl)borate contained 1.9–2.3 moles of ether and
0.9–1.1 mole of water.
P. Laszlo and A. Mathy, Helv. Chim. Acta, 70, 577 (1987).
N. Mine, Y. Fujiwara, and H. Taniguchi, Chem. Lett., 1986,
357.
Friedel–Crafts reaction was tried by using 3c which has two
reaction sites, benzylic chloride and benzylic mesylate moieties,
only the mesylate site reacted to give 4-chloromethylbenzylben-
zene in an excellent yield. This shows selective Friedel–Crafts
benzylation reaction of aromatic compounds to be performed
by the present 1-catalyzed reactions.
8
9
10 I. Hachiya, M. Moriwaki, and S. Kobayashi, Bull. Chem. Soc.
Jpn., 68, 2053 (1995).
11 N. Whittaker, J. Chem. Soc., 1953, 1646.
A typical experimental procedure is described for the reac-
tion of benzene with benzyl chloride (Table 1, entry 7): to a