COMMUNICATION
exhibits the best catalytic ability (Table 1, entries 1–6). In
the presence of bathophen (30 mol%) and KOtBu
(3.0 equiv), such an arylation between 3-iodotoluene (1b)
and 2a takes place at 1108C and the product 3ab is ob-
tained in 90% yield (Table 1, entry 6). The reaction has the
same outcome as the Mizoroki–Heck cross-coupling,[8] how-
ever, it proceeds through an organocatalytic radical process
in the absence of any additional transition-metal catalysts.
Although the previous studies indicated that the arylation of
aryl halides with benzene ran smoothly at 80–1008C,[7] ben-
zene is found as the best solvent in this report (see Table 1,
entry 6 and entries 13–16), with only a trace amount of
biaryl as the byproduct. This result indicates that the aryla-
tion of olefination is highly preferred. It is noteworthy that
when lowering the amount of 2a, or diluting the reaction
mixture, the yields of 3ab diminish and the amount of the
competitive phenylation byproduct increases (Table 1, en-
tries 8 and 9). Lowering the amount of bathophen or tem-
perature or shortening the reaction time leads to an incom-
plete conversion (Table 1, entry 7, 10, and 11). Moreover,
the absence of bathophen terminates the reaction (Table 1,
entry 12).
Various aryl halides were further investigated (Scheme 2).
Para-electron-donating substitutents gave the products in
moderate yields (compounds 3aa, 3ac, and 3ag), whereas
the meta-methoxy substituent shows the worst reactivity
(compound 3ae). o-Iodoanisole exhibits an exceptional re-
activity and the desired product 3af is isolated in 84% yield.
The meta-methyl substituent (3ab) promotes the efficiency a
great deal, however, this cannot be well explained at this
stage. Other substitutents, for example, naphthyl (3ah),
phenyl (3ai), and less reactive halides (such as Cl and F,
compounds 3aj, 3ak, and 3al) are well tolerated, offering
the potential for further orthogonal functionalizations.[9]
Heterocyclic iodides are also suitable, albeit with slightly
lower efficacy (compounds 3am and 3an). Notably, aryl bro-
mides with either electron-donating or electron-withdrawing
groups, for example, 4-bromoanisole and 1-bromo-3-fluoro-
benzene (compounds 3aa, X=Br, and 3al), are suitable;
however, the relatively low efficacy may arise from the
À
lower reactivity of C Br bond.
Other alkene derivatives were surveyed (Scheme 3). The
presence of different substituents on aryl group does not
affect the efficiency significantly and the desired products 3
are obtained in good to excellent yields (3ab–3gb). Howev-
er, different geminal aryl substituents induce a mixture of
two stereoisomers, which cannot be separated by chroma-
tography due to their similar polarities (3cb–3gb). The elec-
tronic and steric effects influence the ratio of two isomers
(see Scheme 3, compounds 3eb to 3 fb and 3gb). Similarly,
the compatibility of OMe, Cl, and F provides the potential
for further functionalization (Scheme 3, 3bb–3db).[8–10] No-
tably, styrene is also a good substrate and only the trans
isomer (3hb) is obtained in 60% yield, which shows the
same selectivity as the traditional Mizoroki–Heck reac-
tion.[8b] Unfortunately, aliphatic alkenes are not suitable for
this transformation.
We further explored the intramolecular radical cyclization
to construct heterocycles. Starting from easily available
ortho-iodophenyl allyl ether 4, the 3-substituted benzofurans
5 are produced in good yields (Scheme 4). During this trans-
formation, a C=C migration takes place to produce thermo-
Scheme 3. Direct arylation of various alkenes with 1b. The reactions
were carried out in the scale of 0.5 mmol of 1b in the presence of catalyst
(0.3 equiv), 2 (3.0 equiv) and KOtBu (3.0 equiv) in benzene (1 mL) in
sealed Schlenk tubes for 36 h. All the yields are those of the isolated
products. For 3eb, 3 fb, 3cb, 3gb, and 3db, the yield is a total of two iso-
mers and the exact ratio of two isomers could not be determined because
the two isomers are unknown compounds and their separation is difficult.
For 3hb, 10 equiv of styrene was added in this reaction.
Scheme 2. Direct arylation of 2a with various aryl halides. The reactions
were carried out in the scale of 0.5 mmol of 1 in the presence of catalyst
(0.3 equiv), 2a (3.0 equiv) and KOtBu (3.0 equiv) in benzene (1 mL) in
sealed Schlenk tubes for 36 h. All the yields are those of the isolated
products.
Chem. Eur. J. 2011, 17, 10844 – 10847
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
10845