Angewandte
Communications
Chemie
[a]
À
Table 1: Optimization of 2-fold C H arylation.
tailored triphenylene synthesis typically require laborious
prefunctionalization steps. Therefore, the development of
concise synthetic strategies to provide triphenylene frame-
works from unactivated substrates is an important synthetic
goal in graphene chemistry.
Herein, we show that unactivated and readily available
arene substrates can undergo Pd-catalyzed 2- or even 4-fold
Entry
Deviations from standard conditions
Yield [%][b]
À
C H arylation to afford substituted triphenylenes 3 or
phenanthro[9,10-b]triphenylenes 4, respectively (Scheme 1c).
To our knowledge, this is the first example of a straightforward
p-extension strategy utilized to provide triphenylene frame-
works from acetanilides and benzamides. The N-substituted
triphenylenes obtained are incorporated into an alcohol field-
effect transistor (FET) sensor, which exhibits a rapid and
reversible response.
1
2
3
4
5
6
7
8
none
no Pd2(dba)3
85
0
52
39
55
0
trace
0
Pd2(dba)3 (1.5 mol%)
Pd(PPh3)4 (instead of Pd2(dba)3)
Pd(OAc)2 (instead of Pd2(dba)3)
no NaOAc
NaOAc (1.0 instead of 5.0 equiv)
AgOAc (instead of NaOAc)
KOAc (instead of NaOAc)
K2S2O8 (1.0 equiv) added
air
BHT (1.0 equiv) added
TEMPO (1.0 equiv) added
toluene (instead of ODCB)
DMF (instead of ODCB)
ODCB (2 instead of 4 mL)
2a (1.5 instead of 3.0 equiv)
1008C
9
trace
64
31
Over the last few decades, direct arylation methods have
emerged aided by bench-stable hypervalent iodine com-
pounds.[21,22] It was anticipated that 2, with cyclic geometry,
10
11
12
13
14
15
16
17
18
27
À
has the potential for 2-fold C H arylation of 1 toward
9[c]
trace
0
aromatic annulation (Figure 1). Simple amide moieties were
chosen as the directing groups (DGs) owing to 1) their wide
prevalence in natural products and functional organic materi-
52
als, 2) the effective facilitation of sp2 C H activation,
À
51
8[c]
[a] Reaction conditions: 1a (0.228 mmol), 2a (3.0 equiv), Pd2(dba)3
(5 mol%), NaOAc (5.0 equiv), ODCB (4 mL), 1508C, 24 h under N2
atmosphere; ODCB=1,2-dichlorobenzene, dba=dibenzylidene-
acetone. [b] Isolated yields. [c] Yield determined by GC using n-dodecane
as an internal standard.
reduced yields (entries 10 and 11). The presence of radical
scavengers (butylated hydroxytoluene (BHT) and 2,2,6,6-
tetramethyl-1-piperidinyloxy (TEMPO)) affected the reac-
tion yields drastically (entries 12 and 13), indicating the
potential involvement of a radical pathway. A probable
thermal reduction of Pd(OAc)2 to Pd0 may account for
a moderate yield (55%, entry 5).[23] However, an alternative
mechanistic pathway involving a PdII/PdIV manifold cannot be
ruled out completely.[22,24] When other solvents were used,
such as toluene or N,N-dimethylformamide (DMF), the
reaction did not progress (entries 14 and 15). Reduction of
the reaction volume (2 mL) only caused a moderate drop in
yield (52%, entry 16). Finally, decreasing the concentration of
2a (1.5 equiv, entry 17) and reducing the reaction temper-
ature (1008C, entry 18) led to moderate and poor yields,
respectively.
With the optimized conditions in hand, our subsequent
goal was to investigate the reaction scope. Arenes with ortho-
alkyl groups, including iPr (1a), methyl (1b), and ethyl (1c),
gave good yields of the corresponding triphenylenes. Func-
tional groups with p-electron donors, such as ortho-phenyl
(1d), ortho-fluoro (1e), and ortho-OMe (1 f) were tolerated,
furnishing the annulated products in moderate to good yields.
However, electron-withdrawing trifluoromethyl, cyano, and
nitro groups resulted in poorer reactivity (3ha, 30%; 3ia and
3ja, no product). Pivanilide (1g) with no ortho-substituent
gave a poor yield (3ga, 25%). Subsequently, the 2-fold
arylation was attempted with meta-substituted substrates with
methyl and cyano groups (data not shown), but no product
À
Figure 1. Proposed 2-fold C H arylation mechanism.
and 3) increased processability for FET applications.
In cycle I, cyclic diaryliodonium salt 2 undergoes successive
single-electron reductions by Pd0 to form X-PdII-aryl com-
plex A, as previously suggested by the Glorius group.[23]
Subsequently, cyclopalladation of arene 1 would afford C,
which can undergo reductive elimination to give aryl iodide
D. In cycle II, oxidative addition, concerted metalation–
deprotonation, and subsequent reductive elimination, regen-
erate Pd0 and afford the desired product 3.
To examine the feasibility of this strategy, various reaction
parameters were surveyed. The optimized conditions pro-
vided annulated product 3aa in 85% yield (Table 1). In the
absence of catalyst (entry 2), there was no reactivity. Changes
in the palladium source or catalyst loading caused diminished
yields (entries 3–5). A control reaction without NaOAc
showed no reactivity (entry 6). Other weak bases, such as
AgOAc and KOAc, were ineffective (entries 8 and 9).
Addition of external oxidants, such as K2S2O8 or air, led to
2
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Angew. Chem. Int. Ed. 2017, 56, 1 – 6
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