Mendeleev Commun., 2015, 25, 126–128
Table 1 Screening of the conditions of the rearrangement of imidate 2a
into N,N-diphenylbenzamide 1a.
pounds according to the general procedure and added new
physicochemical characteristics.‡
First of all, imidate 2b that was reported5(b) to fail to undergo
the rearrangement and decompose at 150°C, was successfully
transformed into product 1b in ILs at the same temperature
150°C in 60–63% yield (Table 2, entries 1, 3), while only a small
fraction of reactant 2b decomposed. Moreover, at a temperature
drop to 120°C compound 1b was obtained in 85% yield, however,
the reaction duration increased (entries 2, 4). Evidently, in the
ongoing rearrangement, ILs stabilize the generation of dipolar
intermediates, which promotes their subsequent transformation to
final products 1. Since the rearrangement at 120–150°C proceeds
over a long time, other imidates 2c–f were subjected to the
rearrangement at 180–190°C, i.e., under considerably milder
conditions than those known from literature (see Table 2). The
yields of all final tertiary acyclic amides 1 exceeded 80%.
Structures of the synthesized compounds were established by
a comparison of their melting points and IR, 1H, 13C NMR and
mass spectra with published data. Since the elemental composi-
tions of the initial imidates 2 do not change in the rearrangement
process the most important information about the structure of
compounds 1 was obtained from IR, 13C NMR (appearance of
CO group) and mass spectra. In particular, the molecular ion
of the final products 1 did not differ from that of initial com-
pounds 2, whereas the fragment ions in mass spectra were dif-
ferent, namely, in compounds 2 fragment ions ArO+ were present,
while in compounds 1 fragment ions ArCO+ appeared.
Entry
IL
T/°C
t/h
Isolated yield (%)
1
2
[bmim]BF4
[bmim]PF6
190
190
190
180
180
180
150
120
150
120
190
190
2.0
1.5
88
90
78
30a
38a
0b
3
[bdmim]BF4
[emim]CF3SO3
[bmpyrr]CF3SO3
[emim]HSO4
[bmim]BF4
[bmim]BF4
[bmim]PF6
2.0
4
1.7
5
2.0
6
2.0
7
14.0
24.0
12.0
22.0
2.0
85
90
87
85
90
90
8
9
10
11c
12c
[bmim]PF6
[bmim]BF4
[bmim]BF4
2.0
aAnd the products of decomposition. b Only products of decomposition.
c Recovered IL.
perature and reaction time were varied. A temperature of 190°C
[60–86°C lower than in refs. 5(f),(g)] was selected to begin with.
The reaction termination was TLC controlled. Among the tested
ILs (entries 1–6, ILs are substrate-specific media), [bmim]BF4
and [bmim]PF6 appeared the best for the processing at this tem-
perature – the reaction was complete within 1.5–2.0 h (entries 1, 2).
Ionic liquid [bdmim]BF4 is also suitable, however the yield of
the final product was lower (entry 3). The other ILs proved to
be inefficient. In ILs with CF3SO3– anion (entries 4, 5) reactant
2a partially gives the target product and the remaining part is
decomposed. The total decomposition of imidate 2a is observed
in acidic IL [emim]HSO4 (entry 6). Lowering temperatures to
150 and even to 120°C did not stop the reaction, however,
longer time, 12–14 and 22–24 h, respectively, was required
(entries 7–10). This is the first instance of the Chapman rear-
rangement at 120°C. After the final product isolation, IL was
recovered and recycled in the same reactions at least twice
without a decrease in the yield of 1a (entries 11, 12).
In conclusion, we have developed a new metal-free approach
for the synthesis of the tertiary acyclic amides by the Chapman
rearrangement of imidates in ILs [bmim]BF4(PF6). The use of ILs
as reaction media promoted acceleration of the rearrangement,
N,N-Diarylbenzamides 1a–g (general procedure). The solution or
suspension of the imidate 2 (2 mmol) in 2 g of corresponding IL was
heated at corresponding temperature (see Table 2) and stirred until dis-
appearance of the reactant (TLC monitoring, eluent CH2Cl2). Then the
reaction mixture was cooled to room temperature, CH2Cl2 (1.5 ml) was
added and the obtained N,N-diarylbenzamide 1 was extracted with Et2O
(5×10 ml). The ethereal extract was stirred with 1 g of absorbent carbon,
filtered, Et2O was evaporated from the filtrate in vacuo and the residue
was crystallized from corresponding solvent. The IL was dried in vacuo
from the solvents remainders and repeatedly used several time in the next
syntheses of the same product without lowering the yield.
The optimal conditions were applied to the Chapman rear-
rangement of other imidates 2b–g (Table 2). Imidates 2, except
for 2d, are known compounds, however, the methods for their
preparation had some distinctions and the most part of them were
insufficiently characterized. We have synthesized these com-
N,N-Diphenylbenzamide 1a: mp 177–178°C (EtOH) (lit.,4(b) 179–180°C).
13C NMR, d: 120.4, 121.8, 124.6, 127.1, 128.9, 131.9, 135.1, 138.1 (Ar),
165.9 (C=O). IR (KBr, n/cm–1): 1656 (C=O), 1600, 1536, 1493, 1439, 1323,
1261, 751, 691. MS, m/z (%): 273 [M+] (20), 180 (5), 168 [M+ – PhCO]
(21), 105 [PhCO] (100), 77 [Ph] (40).
N-(4-Nitrophenyl)-N-phenylbenzamide 1b (prepared from imidates 2b
and 2d): mp 123–124°C (EtOH) (lit.,4(b) 124–125°C). IR (KBr, n/cm–1):
1656 (C=O), 1600, 1535, 1439, 1322, 1261, 750, 691. MS, m/z (%): 318
[M+] (54), 272 [M+ – NO2] (8), 197 [M+ – PhCONH2] (35), 180 [M+ –
– NO2C6H4NH2] (52), 139 [NO2C6H4NH2 + 1] (26), 105 [PhCO] (100),
77 [Ph] (76).
4-Methylphenyl N-phenylbenzimidate 2c: mp 58–59°C (EtOH) (lit.,5(e)
1
58.8–59.8°C). H NMR, d: 2.33 (s, 3H, Me), 6.90–7.85 (m, 14H, Ar).
IR (KBr, n/cm–1): 1659, 1594, 1506, 1263, 1236 (ArO), 1199, 1163. MS,
m/z, (%): 288 [M+ + 1] (3), 180 [M+ – MeC6H4OH + 1] (95), 105 [PhCO]
(12), 77 [Ph] (100).
Phenyl N-(4-nitrophenyl)benzimidate 2d: mp 80–81°C (EtOH). 1H NMR,
d: 6.95–7.30 (m, 10H, Ar), 7.55–7.62 (m, 2H, Ar), 8.02–8.15 (m, 2H,
Ar). 13C NMR, d: 125.5, 126.3, 127.0, 127.8, 128.8, 129.8, 130.5, 131.0,
132.2, 136.3, 142.6, 145.6. IR (KBr, n/cm–1): 1663, 1600, 1512, 1268,
1244, 1206 (PhO), 1169. MS, m/z (%): 318 [M+] (8), 272 [M+ – NO2] (2),
225 [M+ – PhOH + 1] (100), 195 [M+ – PhNO2] (17), 101 [M+ – PhOH –
– PhNO2] (29).
N-(4-Methylphenyl)-N-phenylbenzamide 1c: mp 91–92°C (EtOH)
(lit.,4(b),5(g) 89–90°C). IR (KBr, n/cm–1): 1656 (C=O), 1599, 1513, 1439,
1265, 750, 691. MS, m/z (%): 212 [MeC6H4NH – COPh + 1] (66), 197
[PhNH – COPh] (28), 105 [PhCO] (62), 77 [Ph] (100).
Phenyl N-(4-methoxyphenyl)benzimidate 2e: mp 66–67°C (MeOH)
(lit.,1 66–67°C). Other spectral data (1H NMR, 13C NMR, IR, MS) are
consistent with reported ones.12
N-(4-Methoxyphenyl)-N-phenylbenzamide 1e: mp 119°C (EtOH) (lit.,4(b)
119–120°C). IR (KBr, n/cm–1): 1653 (C=O), 1593, 1521, 1436, 1267, 742,
693. MS, m/z (%): 303 [M+] (22), 198 [M+ – PhCO] (35), 105 [PhCO]
(100), 77 [Ph] (42).
Phenyl 4-methoxy-N-phenylbenzimidate 2f: mp 84–87°C (EtOH) (lit.,13
84–86°C). 1H NMR, d: 3.67 (s, 3H, Me), 7.10–7.85 (m, 14H, Ar).
IR (KBr, n/cm–1): 1657, 1596, 1510, 1260, 1233, 1207 (PhO), 1165.
MS, m/z (%): 287 [M+] (6), 194 [M+ – PhOH + 1] (100), 91 [MeC6H4] (41).
Phenyl 4-nitro-N-phenylbenzimidate 2g: mp 101–102°C (EtOH) (lit.,5(b)
101–102.5°C). 1H NMR, d: 6.92–8.15 (m, 14H, Ar). 13C NMR, d: 126.3,
126.9, 127.9, 129.3, 129.8, 130.1, 130.9, 131.3, 136.5, 143.4, 145.8.
IR (KBr, n/cm–1): 1660, 1588, 1512, 1351, 1223 (PhO). MS, m/z (%):
318 [M+] (65), 272 [M+ – NO2] (16), 224 [M+ – PhOH] (100), 122
[PhNO2] (38).
4-Methoxy-N,N-diphenylbenzamide 1f: mp 139–140°C (EtOH) (lit.,4(b)
140–141°C). IR (KBr, n/cm–1): 1658 (C=O), 1600, 1515, 1436, 1265, 753,
690. MS, m/z (%): 303 [M+] (14), 184 [M+ – 4-MeOC6H4CO] (27), 135
[4-MeOC6H4CO] (100), 107 (37).
4-Nitro-N,N-diphenylbenzamide 1g: mp 155–156°C (EtOH) (lit.,14
156–157°C). IR (KBr, n/cm–1): 1660 (C=O), 1591, 1532, 1435, 1322,
1264, 752. MS, m/z (%): 318 [M+] (81), 272 [M+ – NO2] (19), 224 [M+ –
– PhOH] (47), 150 [4-NO2C6H4CO] (100), 122 [PhNO2] (38).
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