T. Saeki et al.
Bull. Chem. Soc. Jpn., 78, No. 9 (2005) 1657
chromatography on silica gel (Rf ¼ 0:65, hexane as an eluent)
to afford 4-iodomethylbenzene 6 (X ¼ Me) (46 mg, 0.21 mmol;
70%) as colorless oil. 1H NMR ꢁ 1.89 (s, 3H), 6.50 (d, J ¼ 8:0
Hz, 2H), 7.44 (d, J ¼ 8:0 Hz, 1H). 2-Methoxy-4-nitrophenyl-
amine (1) (45 mg, 0.27 mmol; 90%) was recovered by flushing
the silica gel with polar solvent [Rf ¼ 0:25, hexane/AcOEt
(2:1) as an eluent].
A Typical Procedure for the Arylation of 1,3-Diaryl-
triazenes. To a solution of 3 (X ¼ Me) (86 mg, 0.30 mmol),
4-methoxyphenylboronic acid (71 mg, 0.60 mmol), and Pd(OAc)2
through the coupling process (Entries 7 and 9), while the silyl
ether at the para-position and acetal protection reverted back
to phenol and carbonyl moiety, respectively, during the purifi-
cation (Entries 6 and 8).
A similar cross-coupling reaction of the 1,3-diaryltriazene 3
(X ¼ Me) with 4-methoxyphenyltrifluorosilane in the absence
of the extra Lewis acid was also carried out to afford the biaryl
7 in 43% GC yield.6
Azo-Coupling with Silyl Enol Ether. Another example is
the reaction of the 1,3-diaryltriazene 3 (X ¼ Me) with the di-
methylketene methyl trimethylsilyl acetal in the presence of
boron trifluoride (Scheme 5).16 The corresponding ꢀ-arylazo
ester 9 was obtained in 82% yield together with an almost
quantitative recovery of the arylamine 1. The ꢀ-azo carbonyl
compounds can be easily converted to the corresponding ꢀ-
amino derivatives by simple hydrogenation using a Pd/C cat-
alyst.16,17 It is noted again that the arylamine 4 (X ¼ Me) was
practically diazotized by the treatment with the diazonium-
transfer agent 2 and the controlled tautomerism of the resulting
diaryltriazene 3 (X ¼ Me) to afford the arylazo adduct 9.
In summary, we realized the tautomerism control of the un-
symmetrical 1,3-diaryltriazenes by the introduction of the 2-
methoxy-4-nitrophenyl group as one of the two aryl substitu-
ents. The iodination and palladium-catalyzed arylation of the
diaryltriazenes readily proceeded in the presence of boron tri-
fluoride to afford the corresponding aryl iodides and biaryls,
respectively, thus providing a deaminative transformation
process of primary arylamines without direct diazotization.
(3.5 mg, 0.015 mmol) in MeOH (3.0 mL) was added BF3 OEt2
ꢂ
(38 mL, 0.30 mmol) dropwise at room temperature and the mixture
was stirred for 3 h. After quenching with water, the mixture was
extracted with diethyl ether three times and the combined organic
layer was washed with brine and dried over anhydrous magnesium
sulfate. After filtration and evaporation under reduced pressure,
the remaining crude product was purified by column chromatogra-
phy on silica gel [Rf ¼ 0:48, hexane/AcOEt (10:1) as an eluent]
to afford 4-methoxy-40-methylbiphenyl (7) (44 mg, 0.22 mmol;
1
76%) as white solids. H NMR ꢁ 2.22 (s, 3H), 3.38 (s, 3H), 6.90
(d, J ¼ 9:0 Hz, 2H), 7.12 (d, J ¼ 8:0 Hz, 2H), 7.48 (d, J ¼ 8:0
Hz, 2H), 7.49 (d, J ¼ 9:0 Hz, 2H).
A Typical Procedure for the Azo-Coupling of 1,3-Diaryl-
triazenes with Silyl Enol Ethers.
To a solution of 3
(X ¼ Me) (86 mg, 0.30 mmol) in MeCN (3 mL) was added di-
methylketene methyl trimethylsilyl acetal (52 mg, 0.30 mmol)
and BF3 OEt2 (38 mL, 0.30 mmol) at room temperature and the
ꢂ
mixture was stirred for 3 h. After quenching with water, the mix-
ture was extracted with diethyl ether three times and the combined
organic layer was washed with brine and dried over anhydrous
magnesium sulfate. After filtration and evaporation under reduced
pressure, the remaining crude product was purified by column
chromatography on silica gel [Rf ¼ 0:49, hexane/AcOEt (4:1)
as an eluent] to afford methyl 2-methyl-2-(4-methylphenylazo)-
Experimental
A Typical Procedure for the Preparation of 1,3-Diaryl-
triazenes. To a solution of p-toluidine (1.07 g, 10.0 mmol)
and potassium carbonate (2.07 g, 15.0 mmol) in water/THF
(1:1) (20 mL) was added a suspension of 2-methoxy-4-nitroben-
zenediazonium chloride (2) [prepared from 2-methoxy-4-nitro-
phenylamine (1) (1.68 g, 10.0 mmol) and sodium nitrite (759
1
propanoate (9) (44 mg, 0.24 mmol; 82%) as yellow oil. H NMR
ꢁ 1.69 (s, 6H), 2.01 (s, 3H), 3.41 (s, 3H), 6.94 (d, J ¼ 8:0 Hz, 2H),
7.83 (d, J ¼ 8:0 Hz, 2H). Anal. Calcd for C12H16N2O2: C, 65.43;
H, 7.32; N, 12.72%. Found: C, 65.39; H, 7.38; N, 12.63%.
X-ray Crystallographic Analysis of 3 (X ¼ OMe). Single
crystals of 3 (X ¼ OMe) suitable for X-ray crystallography were
obtained by recrystallization from DME. Intensity data were col-
lected on a Rigaku Saturn 70 CCD diffractometer with graphite
ꢁ
mg, 11.0 mmol) in hydrochloric acid (3 mol/L, 10 mL) at 0 C]
ꢁ
dropwise at 0 C and the mixture was stirred for 30 min. The re-
sulting mixture was extracted with AcOEt three times and the
combined organic layer was washed with brine and dried over
anhydrous magnesium sulfate. After filtration and evaporation
under reduced pressure, the remaining crude product was purified
by column chromatography on silica gel [Rf ¼ 0:41, hexane/
AcOEt/benzene (4:1:1) as an eluent] to afford 1-(4-methylphen-
yl)-3-(2-methoxy-4-nitrophenyl)triazene 3 (X ¼ Me) (1.99 g,
6.95 mmol; 70%) as yellow solids, which was recrystallized from
ꢀ
monochromated Mo Kꢀ radiation (ꢂ ¼ 0:71070 A). The data
were corrected for Lorentz and polarization effects and secondary
extinction. The crystal structure was solved by the direct method
(SIR92) and a full-matrix least-squares refinement was carried
out. The non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were included but not refined. All calculations were
performed using the Crystal Structure crystallographic software
package. The analytical conditions are summarized in Table S1
(Supporting Information). Crystallographic data have been depos-
ited with Cambridge Crystallographic Data Centre: Deposition
number CCDC-264859 for compound 3 (X ¼ OMe). Copies of
cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge, CB2 1EZ,
UK; Fax: +44 1223 336033; e-mail: deposit@ccdc.cam.ac.uk).
ꢁ
1
hexane/AcOEt (4:1). mp: 165–166 C (dec). H NMR ꢁ 2.14 (s,
3H), 2.88 (s, 3H), 7.09 (d, J ¼ 8:3 Hz, 2H), 7.39 (d, J ¼ 8:7
Hz, 1H), 7.41 (d, J ¼ 2:3 Hz, 1H), 7.68 (d, J ¼ 8:3 Hz, 2H),
7.85 (dd, J ¼ 8:7, 2.3 Hz, 1H). Anal. Calcd for C14H14N4O3: C,
58.73; H, 4.93; N, 19.57%. Found: C, 58.63; H, 4.85; N, 19.59%.
A Typical Procedure for the Iodination of 1,3-Diaryltri-
azenes. To a solution of 3 (X ¼ Me) (86 mg, 0.30 mmol) and
NaI (90 mg, 0.60 mmol) in MeCN (3.0 mL) was added BF3 OEt2
ꢂ
(38 mL, 0.30 mmol) dropwise at room temperature and the mixture
was stirred at 40 ꢁC for 2 h. After quenching with water, the mix-
ture was extracted with diethyl ether three times and the combined
organic layer was washed with brine and dried over anhydrous
magnesium sulfate. After filtration and evaporation under reduced
pressure, the remaining crude product was purified by column
This work was supported by a Grant-in-Aid for COE Re-
search on Elements Science, No. 12CE2005, from the Ministry
of Education, Culture, Sports, Science and Technology, Japan.