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B. P. Cho et al. / Tetrahedron 56 (2000) 7379–7388
filtered to remove the catalyst. The filtrate was concentrated
and partitioned between H2O and ether. The aqueous layer
was extracted with ether (3×50 mL) and the combined ether
extracts were washed with water. The ether layer was dried
over anhydrous MgSO4 and the solution was filtered and
evaporated. The resulting oily residue was applied to a silica
gel column and eluted with ethyl acetate and hexane (1:4).
Appropriate portions were pooled, concentrated and recrys-
tallized from ethyl acetate and hexane to give 894 mg (62%)
of an analytically pure product 2. Mp 114–115ЊC; UV lmax
(log e) 255 nm (4.36), 292 nm (shoulder, 3.57); HPLC
(system 3) tR 18.8 min; ESI-MS m/z 303 (MϩH)ϩ, 288
(MϩϪCH3ϩ1), 211 (MϩϪPhϪCH3ϩ1 or MϩϪ
0.94 mmol) was dissolved in 0.5 mL of 48% aqueous
HBF4 and placed in an ice-bath. An ice-cold solution of
NaNO2 (65 mg, 0.94 mmol) was added dropwise with stir-
ring. The resulting brown viscous residue was filtered and
washed with H2O and transferred to a new flask containing
excess NaNO2 (200 mg) and copper powder (10 mg) in
2 mL of H2O. After stirring for 10 min, the mixture was
treated with 10 mL of 1.0 M NaOH and extracted with
chloroform. The combined organic extracts were washed
with H2O, dried over anhydrous MgSO4, and evaporated.
The crude residue was passed through a short silica gel
column using ethyl acetate/hexane (1:9) as the eluent. A
bright yellow band was collected to give 120 mg of an
1
1
C6H4NH2ϩ1); H NMR d 2.87 (s, 6, dimethyl), 4.44 (bs,
orange solid. According to H NMR and HPLC/ESI-MS
2, NH2, D2O exchangeable), 5.30 (s, 1, benzylic), 6.57 (d, 2,
analyses using HPLC system 3, the product contained an
approximately 3:1 mixture of 6 and 7.
0
0
H3,5, J8.5 Hz), 6.66 (d, 2, H3 ,5 , J8.9 Hz), 6.80 (d, 2,
0
0
H2,6, J8.4 Hz), 6.92 (d, 2, H2 ,6 , J8.8 Hz), 7.12 (m, 2,
H2 ,6 ), 7.14 (m, 1, H4 ), 7.24 (m, 2, H3 ,5 ); 13C NMR d 40.7
(dimethyl), 56.0 (benzylic), 113.2, 115.0, 120.0 (Cq), 126.5,
128.7, 128.9 (Cq), 130.0, 130.5, 130.6, 133.6 (Cq), 133.8
(Cq), 146.7 (Cq); Anal. Calcd for C21H22N2: C, 83.40; H,
7.33; N, 9.26. Found: C, 83.51; H, 7.26; N, 9.13.
4-(N,N-Dimethylamino)-3-aminotriphenylmethane (8).
Compound 6 (100 mg, 0.3 mmol) was treated with
NH2NH2.H2O (100 mL, 2 mmol) and 10% Pd/C (20 mg)
in 20 mL of absolute ethanol and refluxed for 1 h. The
warm solution was filtered, concentrated, and extracted
with ether. The ether extracts were washed with H2O,
dried over anhydrous MgSO4, and evaporated. The residue
was purified by a silica chromatography (ethyl acetate/
hexane1:4) to give an analytically pure product 8 as a
viscous residue (78 mg, 86%). UV lmax (log e) 250 nm
(4.49), 297 nm (4.28); HPLC (system 2) tR 12.4 min; ESI-
MS m/z 303 (MϩH)ϩ, 288 (MϩϪCH3ϩ1), 211
00 00
00
00 00
Attempted nitro-dediazoniation of 2
Method A—using Grivas’ conditions. A solution of 2
(604 mg, 2.0 mmol) in 50% acetic acid (10 mL) was
added dropwise to a solution of NaNO2 (1.38 g, 20 mmol)
in H2O (25 mL) in an ice-bath. The solution turned initially
to an orange color and then a dark brown viscous residue.
After 30 min, the mixture was neutralized by addition of
saturated NaHCO3. The aqueous solution was then extracted
with chloroform three times. The combined organic extracts
were washed subsequently with saturated NaHCO3 and
H2O, and dried over anhydrous MgSO4. The extracts were
evaporated and the residue was subjected to column
chromatography on silica using ethyl acetate and hexane
(1:9) as the eluant. The distinct yellow band was collected
and concentrated to give 225 mg of a bright orange solid,
which is an approximately 3:1 mixture of 6 and 7. The
mixture was separated by semi-prep HPLC using system
2. 6 (128 mg): mp 98–99ЊC (ethyl acetate/hexane); UV
lmax (log e) 253 nm (4.44), 440 nm (3.45); HPLC tR
16.4 min (system 2); ESI-MS m/z 333 (MϩH)ϩ, 315
(MϩϪH2Oϩ1), 299 (MϩϪH2OϪCH4ϩ1); 1H NMR d
2.84 (s, 6, dimethyl), 5.62 (s, 1, benzylic), 7.14 (d, 1, H5,
1
(MϩϪCH3ϪPhϩ1); H NMR d 2.60 (s, 6, dimethyl), 4.40
(bs, 2, NH2, D2O exchangeable), 5.41 (s, 1, benzylic), 6.36
(dd, 1, H6, J8.1, 2.1 Hz), 6.51 (d, 1, H2, J2.1 Hz), 6.87
0
0
00 00
(d, 1, H5, J8.1 Hz), 7.14 (m, 4, H2 ,6 ,2 ,6 ), 7.18 (m, 2,
H4 ,4 ), 7.27 (m, 4, H3 ,5 ,3 ,5 ); 13C NMR d 43.7 (dimethyl),
57.3 (benzylic), 116.5, 119.1, 119.3, 126.8, 128.9, 130.1,
139.3 (Cq), 140.3 (Cq), 142.9 (Cq), 145.5 (Cq); Anal. Calcd
for C21H22N2: C, 83.40; H, 7.33; N, 9.26. Found: C, 83.19;
H, 7.43; N, 9.11.
0
00
0
0
00 00
4-Methylaminotriphenylmethane (9). Compound
7
(39 mg, 0.13 mmol) was reduced as described above for 8.
A usual workup followed by silica column purification gave
a pure product (30 mg, 85 %) as a viscous residue. UV lmax
(log e) 253 nm (4.24), 298 nm (3.41); HPLC (system 2) tR
10.9 min; ESI-MS m/z 274 (MϩH)ϩ, 259 (MϩϪCH3ϩ1),
1
182 (MϩϪCH3ϪPhϩ1); H NMR d 2.74 (s, 3, methyl),
0
0
00 00
0
00
4.81 (bs, 1, NH, D2O exchangeable), 5.45 (s, 1, benzylic),
J8.7 Hz), 7.17 (m, 4, H2 ,6 ,2 ,6 ), 7.23 (m, 2, H4 ,4 ), 7.27
0
0
00 00
6.53 (d, 2, H3,5, J8.6 Hz), 6.87 (d, 2, H2,6, J8.5 Hz), 7.13
(dd, 1, H6, J8.7, 2.3 Hz), 7.32 (m, 4, H3 ,5 ,3 ,5 ), 7.46 (d, 1,
H2, J2.3 Hz); 13C NMR d 42.6 (dimethyl), 56.0 (benzylic),
119.5, 127.1, 127.4, 129.3, 130.1, 134.9, 135.2 (Cq), 144.5
(Cq), 145.5 (Cq); Anal. Calcd for C21H20N2O2: C, 75.88; H,
6.07; N, 8.43. Found: C, 76.03; H, 5.92; N, 8.60. 7 (38 mg):
mp 138–139ЊC (methanol/H2O); direct probe EI-MS m/z
302 (Mϩ, 10%), 272 (MϩϪNO, 100%); HPLC tR 14.5 min
(system 2); UV lmax (log e) 272 nm (3.94); 1H NMR d 3.43
0
0
00 00
0
00
0
0
00 00
(m, 4, H2 ,6 ,2 ,6 ), 7.17 (m, 2, H4 ,4 ), 7.27 (m, 4, H3 ,5 ,3 ,5 );
13C NMR d 30.6 (methyl), 56.9 (benzylic), 112.6, 126.8,
128.9, 130.1, 130.7, 132.4 (Cq), 146.0 (Cq), 150.0 (Cq);
Anal. Calcd for C20H19N: C, 87.87; H, 7.01; N, 5.12.
Found: C, 87.64; H, 7.02; N, 5.10.
N,N-Dimethyltriphenylmethane (10). Route A: Phenyl-
lithium (5.6 mL, 1.8 M in cyclohexane/ether, 10 mmol)
was added dropwise to a solution of 4-(dimethylamino)-
benzophenone (4, 2.25 g, 10 mmol) in dry ether at Ϫ78ЊC
under an argon atmosphere. Upon addition of phenyl-
lithium, the milky white solution turned sequentially to
green, then yellow, and finally clear. The mixture was
warmed to room temperature overnight with stirring. The
mixture was worked up as described for 5 to give 3.69 g of a
00 00
(s, 3, methyl) 5.71 (s, 1, benzylic), 7.19 (m, 4, H2 ,6 ), 7.25
0
00
00 00
(m, 2, H4 ,4 ), 7.29 (m, 2, H2,6), 7.33 (m, 4, H3 ,5 ), 7.57 (m, 2,
H3,5); 13C NMR d 31.4 (methyl), 56.9 (benzylic), 112.0,
127.3, 129.3, 130.1, 131.1, 141.7 (Cq), 144.1 (Cq), 144.7
(Cq); HRMS (CI mode using methane gas) calcd for
C20H19N2O (MϩH)ϩ 303.1497, found 303.1491.
Method B—using HBF4/NaNO2. Compound 2 (284 mg,