(entry 7). Interestingly, combined use of 4 and triphenylphosphine
resulted in formation of octylbenzene in moderate yield (entry 8).
Without any ligands, a 5% yield of octylbenzene was obtained
(entry 9).
ð4Þ
Diethyl ether is the best solvent. The reactions in toluene, THF,
dioxane, and hexane provided octylbenzene in 88, 81, 65, and 64%
yields, respectively, under the NiCl2(1) catalysis.
This work was supported by Grants-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology, Government of Japan.
Other alkyl halides underwent the nickel-catalysed phenylation
with the aid of 1 (eqn (2), Table 2). The reactions of primary alkyl
bromides provided the corresponding phenylated products in high
yields (entries 1,9 4–9). Typical protective groups such as THP and
1,3-dioxolane survived under the reaction conditions (entries 6, 7),
while carbonyl groups were not tolerant. 8-Bromo-1-octene was
phenylated, leaving the terminal olefinic group untouched (entry
9). Primary alkyl iodide was as reactive as bromide (entry 3). In
contrast, alkyl chloride completely resisted the reaction.
Unfortunately, an attempted cross-coupling reaction of a second-
ary alkyl bromide resulted in an unsatisfactory yield of
cyclohexylbenzene (entry 10).
Notes and references
1 Selected examples: phosphine–phosphite ligand for asymmetric hydro-
phosphination, K. Nozaki, N. Sakai, T. Nanno, T. Higashijima,
S. Mano, T. Horiuchi and H. Takaya, J. Am. Chem. Soc., 1997, 119,
4413, aminophosphine ligand, T. Hayashi, K. Yamamoto and
M. Kumada, Tetrahedron Lett., 1974, 15, 4005, phosphinooxazole for
hydrogenation, S. Bell, B. Wu¨stenberg, S. Kaiser, F. Menges,
T. Netscher and A. Pfaltz, Science, 2006, 311, 642.
2 (a) R. Shintani, W.-L. Duan, T. Nagano, A. Okada and T. Hayashi,
Angew. Chem., Int. Ed., 2005, 44, 4611; (b) R. Shintani, W.-L. Duan,
K. Okamoto and T. Hayashi, Tetrahedron: Asymmetry, 2005, 16, 3400.
n
3 Synthesis of 1?BH3: a solution of BuLi in hexane (1.60 M, 8.75 mL,
(2)
14 mmol) was added to a solution of 1,2,3,4,5-pentamethyl-1,3-
cyclopentadiene (2.5 mL, 15 mmol) in THF (50 mL) at 220 uC. The
mixture was stirred for 30 min at the same temperature. Diiodomethane
(0.81 mL, 10 mmol) was added to the reaction mixture, and the mixture
was stirred for 12 h at room temperature. The reaction was quenched
with water, and the mixture was extracted with hexane. The combined
organic parts were washed with brine, dried over anhydrous Na2SO4,
and concentrated in vacuo to give a crude oil. The oil was filtered
through a short pad of silica gel (hexane) to afford 5-iodomethyl-
1,2,3,4,5-pentamethyl-1,3-cyclopentadiene, which was used for the next
step without further purification. A solution of nBuLi in hexane (1.60 M,
5.29 mL, 8.46 mmol) was added to a solution of diphenylphosphine
(1.33 mL, 7.69 mmol) in THF (38 mL) at 0 uC. The mixture was stirred
for 10 min at the same temperature. Cp*CH2I in THF (10 mL) was
added to the reaction mixture, and the mixture was stirred for 3 h at
70 uC. Borane–dimethyl sulfide complex (0.88 mL, 9.23 mmol) was
added to the mixture at 0 uC, and the resulting mixture was stirred for
30 min at 0 uC. The reaction was quenched with water, and the mixture
was extracted with ethyl acetate. The combined organic parts were
washed with brine, dried over anhydrous Na2SO4, and concentrated
in vacuo to give a crude oil. The oil was purified by chromatography on
silica gel (Wakogel C–200, hexane–ethyl acetate = 20 : 1) to afford
1?BH3 (2.02 g, 5.80 mmol, 75%). IR (nujol) 694, 736, 866, 1058, 1436,
2385 cm21; 1H NMR (CDCl3) d (ppm) 0.40–1.20 (br, 3H), 0.98 (d, J =
2.5 Hz, 3H), 1.39 (s, 6H), 1.59 (s, 6H), 2.53 (d, J = 11.0 Hz, 2H), 7.33–
7.56 (m, 10H); 13C NMR (CDCl3) d (ppm) 10.09 (2C), 11.02 (2C), 24.87
(d, J = 13.8 Hz), 31.31 (d, J = 32.9 Hz), 53.51, 128.00 (d, J = 9.5 Hz,
4C), 130.47 (d, J = 2.4 Hz, 2C), 131.12 (d, J = 54.9 Hz, 2C), 132.56 (d,
J = 9.1 Hz, 4C), 135.75 (2C), 138.21 (2C); 31P NMR (CDCl3) d (ppm)
9.08 (m); found: C, 79.11; H, 8.62%. Calcd for C23H30BP: C, 79.32; H,
8.68%. mp: 85.0–85.5 uC.
The cross-coupling reaction is believed to involve a radical
process as justified by the following two experiments. Treatment of
cyclopropylmethyl bromide with p-methoxyphenylmagnesium
bromide furnished p-(3-butenyl)anisole (eqn (3)). No cyclopropane
skeletons were observed in the crude oil. In addition, the reaction
of 6-halo-1-hexene derivative 5 afforded benzyl-substituted pyrro-
lidine 6, in addition to unphenylated pyrrolidine 7 (eqn (4)). Ring-
opening of a cyclopropylmethyl radical and ring-closure of a
5-hexenyl radical are well-known isomerization reactions,10
suggesting the intermediacy of carbon-centered radicals.
Oxidative addition via a single electron transfer process is most
probable.4
ð3Þ
Table 2 Reactions of various alkyl halides with phenylmagnesium
bromidea
4 For reviews: (a) A. C. Frisch and M. Beller, Angew. Chem., Int. Ed.,
2005, 44, 674; (b) J. Terao and N. Kambe, Bull. Chem. Soc. Jpn., 2006,
79, 663; (c) M. R. Netherton and G. C. Fu, Adv. Synth. Catal., 2004,
346, 1525; (d) A. Fu¨rstner and R. Martin, Chem. Lett., 2005, 34, 624; (e)
H. Yorimitsu and K. Oshima, Pure Appl. Chem., 2006, 78, 441; (f)
H. Ohmiya, H. Yorimitsu and K. Oshima, J. Am. Chem. Soc., 2006,
128, 1886 and references cited therein; (g) R. B. Bedford, M. Betham,
D. W. Bruce, S. A. Davis, R. M. Frost and M. Hird, Chem. Commun.,
2006, 1398 and references cited therein.
5 The reactions in ref. 4b and 4c use 1,3-butadiene and pyridine
derivatives, respectively, as a ligand. Nickel-salen complexes catalysed
the phenylation of alkyl bromide: P. Styring, C. Grindon and C.
M. Fisher, Catal. Lett., 2001, 77, 219.
Entry
Substrate
X eq.
Isolated yield (%)
1
2
3
4
5
6
7
8
9
nC8H17Br
nC8H17Br
1.50
1.50
1.75
1.75
1.75
1.75
2.50
3.00
2.00
1.50
83
84b
80
60
70
76
76
68
62
36
nC12H25
I
PhCH2CH2Br
PhCH2CH2CH2Br
THPO(CH2)5Brc
(OCH2CH2O)CH(CH2)4Br
Br(CH2)6Br
CH2LCH(CH2)6Br
10
a
cC6H11Br
6
31P NMR analysis of a mixture of Ni(cod)2 and 1 in C6D6 showed one
clean signal at d = 38.38 ppm. A 31P signal of 1 alone appeared at
d = 223.58 ppm. We are tempted to conjecture the formation of a
nickel–phosphine complex. However, there remains a possibility that
Reaction conditions are shown in eqn (2). Ligand 1 was generated
b
in situ by treatment of 1?BH3 with DABCO. p-MeOC6H4MgBr
c
was used instead of PhMgBr. THP = Tetrahydropyranyl.
This journal is ß The Royal Society of Chemistry 2006
Chem. Commun., 2006, 4726–4728 | 4727