Key words copper-catalysis - three-component reaction -
O -fluoroalkylisourea - 2-alkoxybenzimidazole - C–H activation
Isoureas, an important class of versatile organic reagent, have been widely used as
guanylating and alkylating agents.[1 ] Additionally, they are key precursors for constructing various bioactive molecules,
such as the hypertension drug Candesartan,[2 ] glucocerebrosidase inhibitor fused oxazolidin-2-imines and nanomolar enzyme activity
enhancer spiro oxazolidin-2-imines.[3 ] Despite their widespread applications, only a limited number of synthetic routes
to isoureas have been reported, mainly relying on nucleophilic addition of alcohols
to carbodiimides (Scheme [1, a ]). Initially, thermal acid- or base-promoted reactions were developed by Stieglitz[4 ] and Dains,[5 ] which are only suitable for the synthesis of N -arylisoureas. Subsequently, copper and zinc catalysts were used to promote the reaction
by Däbritz[6 ] and Schmidt,[7 ] respectively, providing more efficient routes for the preparation of both N -arylisoureas and N -alkylisoureas. Recently, uranium and thorium amide catalysts have also been applied
to the reaction, which is reported by Eisen to be a highly efficient synthetic protocol.[8 ] These approaches are all similar, and more diverse methodologies involving simple
and easily available starting materials are clearly required for the synthesis of
isoureas.
Scheme 1 Approaches to the synthesis of isoureas
Inspired by our work on transition-metal-catalysed multicomponent reactions for the
synthesis of N -molecules,[9 ] we have recently developed a copper-catalysed, three-component reaction of cyanamides,
amines and diaryliodoniums for the synthesis of guanidines. Here, an extension of
this methodology to fluroloalcohols was explored for the rapid synthesis of O -fluoroalkylisoureas that can be useful synthons for potentially bioactive cyclic
fluoro-isoureas[10 ] (Scheme [1, b ]).
We started our study by investigating the reaction of p -tolylcyanamide (1a ), di(p -tolyl)iodonium triflate (2a ) and 2,2,2-trifluoroethanol (3a ) in the presence of K2 CO3 using CuCl (5 mol%) as catalyst with bipy (2,2′-bipyridyl) in toluene at 80 °C under
N2 for 2 h (Table [1 ], entry 1). Gratifyingly, the reaction afforded the desired isourea 4a in 62% yield, and the reaction under air produced 4a in 47% yield (entry 2). The reaction conditions including bases, solvents, ligands,
and copper catalysts were then screened in detail (Table [1 ]). Other bases such as NaHCO3 , Cs2 CO3 , K3 PO4 , t -BuOK and Et3 N all afforded inferior yields (entries 3–7), and the reaction without base did not
produce any product (entry 8).
Table 1 Optimization of Reaction Conditionsa
Entry
Base
Solvent
L
Cat.
Yield (%)b
1
K2 CO3
toluene
Bipy
CuCl
62
2c
K2 CO3
toluene
Bipy
CuCl
47
3
NaHCO3
toluene
Bipy
CuCl
22
4
Cs2 CO3
toluene
Bipy
CuCl
52
5
K3 PO4
toluene
Bipy
CuCl
33
6
t -BuOK
toluene
Bipy
CuCl
46
7
Et3 N
toluene
Bipy
CuCl
28
8
–
toluene
Bipy
CuCl
0
9
K2 CO3
dioxane
Bipy
CuCl
26
10
K2 CO3
DMSO
Bipy
CuCl
20
11
K2 CO3
H2 O
Bipy
CuCl
25
12
K2 CO3
DMF
Bipy
CuCl
22
13
K2 CO3
THF
Bipy
CuCl
31
14
K2 CO3
toluene
1,10-Phen
CuCl
31
15
K2 CO3
toluene
PPh3
CuCl
61
16
K2 CO3
toluene
–
CuCl
65
17
K2 CO3
toluene
–
CuBr
54
18
K2 CO3
toluene
–
CuI
53
19d
K2 CO3
toluene
–
CuCl
64
20
K2 CO3
toluene
–
–
0
21e
K2 CO3
toluene
–
CuCl
51
22f
K2 CO3
toluene
–
CuCl
48
a Reaction conditions: p -tolylcyanamide 1a (0.3 mmol), di(p -tolyl)iodonium triflate 2a (0.3 mmol), 2,2,2-trifluoroethanol 3a (0.2 mmol), copper salt (0.01 mmol), solvent (1.0 mL), stirred under N2 , 80 °C, 2 h.
b Isolated yield.
c The reaction was performed under air.
d CuCl (0.02 mmol) was used.
e Ratio 1a /2a /3a =1:1.5:1.5.
f Ratio 1a /2a /3a =1:1:1.5.
Replacing toluene with other solvents such as dioxane, DMSO, H2 O, DMF or THF did not improve the reaction yield (Table [1 ], entries 9–13). The reactions with 1,10-phen or PPh3 as ligands did not provide higher yields (entries 14 and 15), and the reaction without
ligand afforded a slightly higher yield (entry 16). Other catalysts such as CuBr and
CuI were inferior to CuCl (entries 17 and 18). Increasing the amount of CuCl (10 mol%)
did not enhance the reaction yield (entry 19), and the absence of copper catalyst
led to no desired isourea formation (entry 20). Finally, the substrate ratios (1a /2a /3a =1.5:1.5:1, 1:1.5:1.5, 1:1:1.5) were explored (entries 16, 21 and 22), and the 1a /2a /3a =1.5:1.5:1 ratio was found to be optimal.
With the optimised reaction conditions in hand, the scope of the reaction with respect
to cyanamide was evaluated (Scheme [2 ]). Phenylcyanamide gave 65% yield of 4b , and m - and o -tolyl cyanamides also formed the corresponding isoureas 4c and 4d , respectively, in good yields. Arylcyanamides with either electron-withdrawing or
electron-donating groups likewise provided 4e and 4f in comparably good yields. Impressively, 1-nathylcyanamide afforded the desired product
4g in high yield. Additionally, some aliphatic cyanamides were found to be suitable
for the reaction. However, low yields were obtained for aliphatic cyanamides, as
the cross-coupling products of the aliphatic cyanamides and di(p -tolyl)iodonium triflate were found to be major products.[11 ] For instance, benzylcyanamide and cyclohexylcyanamide both produced the corresponding
isoureas 4h and 4i with 24% and 20% yield, respectively, and t -butylcyanamide did not afford any of desired product 4j , which is probably due to the extreme steric hindrance of the t -butyl group.
Scheme 2 Scope of the reaction with respect to cyanamide. Reagents and conditions : Cyanamide 1 /diaryliodonium triflate (2a or 2b )/2,2,2-trifluoroethanol 3a [1 /2a (or 2b )/3a =1.5:1.5:1.0], CuCl (0.05 equiv), K2 CO3 (2.25 equiv).
A variety of the diaryliodonium triflates was then examined, as shown in Table [2 ]. Symmetric diaryliodoniums with either electron-poor or electron-rich aryls produced
the desired isoureas in good yields (entries 1–4). For example, di(p -chrolophenyl)iodonium triflate and di[p -(t -butyl)phenyl]iodonium triflate gave 63% and 55% yield, respectively (entries 2 and
4). The reactions of sterically hindered di(2,5-dimethylphenyl)iodonium triflate and
di(2,4,6-trimethylphenyl)iodonium triflate furnished the desired products in higher
yields (entries 5 and 6), because the side reactions between cyanamides and sterically
hindered diaryliodoniums were reduced. For the unsymmetrical diaryliodonium triflates,
the reactions provide good yields comparable to those with symmetrical diaryliodoniums
triflates. The phenyliodonium triflates with p -(t -butyl)phenyl and p -iodophenyl both afforded a mixture of products with low chemoselectivities (entries
7 and 8). Interestingly, phenyl(p -NO2 -phenyl)iodonium only produced a single product 4q′ in low yield (entry 9). Phenyl(2,5-dimethylphenyl)iodonium triflate yielded two products
4n and 4n′ in 1.7:1 ratio (entry 10). These results suggest that the more electron-rich and
bulkier aryl groups of the unsymmetrical diaryliodoniums were preferable transferred
in this three-component reaction.
Table 2 Scope of the Reaction with Respect to Diaryliodonium Triflatea
Entry
Ar1
Ar2
4 /4′ (ratio)
Yield (%)b
1
C6 H5
C6 H5
4b /– (–)
67
2
4-ClC6 H4
4-ClC6 H4
4k /– (–)
63
3
4-BrC6 H4
4-BrC6 H4
4l /– (–)
35
4
4-(t -butyl)C6 H4
4-(t -butyl)C6 H4
4m /– (–)
55
5
2,5-(CH3 )2 C6 H3
2, 5-(CH3 )2 C6 H3
4n /– (–)
76
6
2,4,6-(CH3 )3 C6 H2
2, 4, 6-(CH3 )3 C6 H2
4o /– (–)
73
7
4-(t -butyl)C6 H4
C6 H5
4m /4m′ (1.5:1)c
64
8
4-IC6 H4
C6 H5
4p /4p′ (1:1.1)c
61
9
4-NO2 C6 H4
C6 H5
4q /4q′ (0:1)
32
10
2,5-(CH3 )2 C6 H3
C6 H5
4n /4n′ (1.7:1)
70
a Reaction conditions: p -tolylcyanamide 1a /diaryliodonium triflate 2 /2,2,2-trifluoroethanol (3a ) (1a /2 /3a =1.5:1.5:1.0), CuCl (0.05 equiv), K2 CO3 (2.25 equiv).
b Isolated yield.
c Ratio based on 1 H NMR spectroscopic analysis.
Finally, the scope of the reaction with respect to alcohol was explored (Scheme [3 ]). We were pleased to find that the protocol was tolerant of many fluorine-substituted
alcohols. Both mono- and di-fluoroethanols delivered the corresponding products 4r and 4s in 49% and 63% yield, respectively. 1,1,1,3,3,3-Hexafluoro-2-propanol furnished the
desired product 4t in moderate yield (51%).
Scheme 3 Scope of the reaction with respect to fluoroalcohol. Reagents and conditions : p -tolylcyanamide 1a /di(p -tolyl)iodonium triflate 2a /alcohol 3 (1a /2a /3 =1.5:1.5:1.0), CuCl (0.05 equiv), K2 CO3 (2.25 equiv). a With di(p -tolyl)cyanamide, yield based on 1 H NMR spectroscopic analysis.
Moreover, ethanol was found to be suitable for the reaction, although a low yield
of 4u was obtained (34%), indicating that fluorine plays an important role in activation
of the alcohol (4r vs. 4s vs. 4u ). The reaction of phenol was complex, with formation of unidentified products.
Considering 2-alkoxybenzimidazole is the core of the hypertension drug candesartan,[2 ] the C–H activation of the isoureas was explored for the synthesis of 2-fluoroalkoxybenzimidazoles,
which may have interesting bioactivities (Scheme [4 ]).[10 ]
Scheme 4 PhI(OAc)2 -promoted C–H activation of isoureas for the synthesis of 2-alkoxybenzimidazoles
We were pleased to find that the C–H activation of isourea 4a can be mediated by PhI(OAc)2 to form 2-(2,2,2-trifluoroethoxy)benzimidazole 5a in 91% yield at room temperature. The mild reaction conditions of this protocol mean
that it could potentially have wide application.
Control experiments were also carried out for mechanistic studies. Nucleophilic addition
of p -tolylcyanamide (1a ) and 2,2,2-trifluoroethanol (3a ) did not take place under the optimal conditions, with most of the p -tolylcyanamide being recovered (Scheme [5a ]).
Scheme 5 Control experiments for mechanistic insight
In addition, the nucleophilic addition product 6 was a not detected during the three-component reaction. Together, these results suggest
that the reaction pathway involving nucleophilic addition of cyanamide 1 and fluoroalcohol 3 followed by C–N coupling with diaryliodonium triflate 2 is unlikely (Scheme [6, a ]).
Scheme 6 Proposed reaction mechanism
The addition of the radical inhibitor 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)
did not reduce product formation (Scheme [5, b ]), ruling out a radical process.[12 ] Thus, a plausible pathway is proposed (Scheme [6, b ]), involving oxidative addition of diaryliodonium triflate 2 with CuCl,[13 ] followed by coordination with cyanamide 1 and isomerisation promoted by K2 CO3 to form intermediate D . Then, D may undergo reductive elimination and nucleophilic addition with fluoroalcohol 3 to generate the desired product 4 via intermediate E or F . The N-arylation products of diarylcyanamides have been proposed as intermediates
for the copper-catalysed, three-component reaction of diarylcyanamides, diaryliodoniums
and H2 O.[14 ] However, the N-arylation product E is barely detected in this reaction. Thus, it is reasonable to conclude that the
desired product is produced via intermediate F .
In summary, an efficient cooper-catalysed, three-component reaction of cyanamide,
fluoroalcohol and diaryliodonium triflate has been developed for the synthesis of
O -fluoroalkylisoureas in good yields. The use of simple and readily available starting
materials is a major practical advantage of this protocol. In addition, the PhI(OAc)2 -promoted C–H activation of O -fluoroalkoxyisoureas provides a convenient access to potentially valuable 2-fluoroalkoxybenzimidazoles.
Further exploration of such three-component reactions to expand the diversity of this
methodology is under way in our laboratory.
1 H NMR spectra were recorded at 400 MHz or 500 MHz with a Bruker AC-500 spectrometer.
13 C NMR spectra were similarly recorded at 101 MHz or 125 MHz. Chemical shifts (δ) are
reported in parts per million (ppm) relative to residual proton signals in CDCl3 (δ = 7.26, 77.00 ppm). Coupling constants (J ) are reported in Hertz (Hz) and refer to apparent multiplicities; the following abbreviations
are used: s (singlet), d (doublet), t (triplet), q (quartet), quin (quintet), sept
(septet), hept (heptet), m (multiplet), br (broad signal). Because of the presence
of tautomers, we found that some 13 C NMR signals were barely detectable for some isoureas, guanidines,[14 ] and isothioureas;[15 ] only clear signals are reported. Additionally, the total number of 13 C NMR signals is more than the total number of non-equivalent carbon atoms in some
isoureas, which may be due to the presence of E /Z isomers. Mass spectra were obtained either from an LCMS-IT-TOF (ESI or APCI) using
positive or negative electron spray (ES+ or ES– ), or from high-resolution mass spectra (HRMS). Flash chromatography was performed
using SDS silica gel 60 (35–70 μm). Preparative thin-layer chromatography (TLC) was
carried out on 20 × 20 cm plates with a layer thickness of 0.5 or 1 mm (SDS Silicage
l60 F254).
All reagents were obtained from commercial suppliers unless otherwise stated. When
necessary, organic solvents were routinely dried and/or distilled prior to use and
stored over molecular sieves under argon. The starting cyanamides[16 ] and diaryliodonium triflates[17 ] are known and were prepared according to the reported procedures.
Synthesis of O-Fluoroalkylisoureas through Copper-Catalysed, Three-Component Reaction
of Cyanamides, Fluoroalcohols and Diaryliodonium Triflates; General Procedure
Synthesis of O-Fluoroalkylisoureas through Copper-Catalysed, Three-Component Reaction
of Cyanamides, Fluoroalcohols and Diaryliodonium Triflates; General Procedure
To a round-bottom sidearm flask, CuCl (0.01 mmol, 0.05 equiv), cyanamide 1 (0.3 mmol, 1.5 equiv), diaryliodonium triflate 2 (0.3 mmol, 1.5 equiv), and K2 CO3 (0.45 mmol, 2.25 equiv) were sequentially added, and the vessel was degassed and
backfilled with nitrogen (balloon). Toluene (1 mL) and fluoroalcohol 3 (0.2 mmol, 1 equiv) were added and the mixture was heated to 80 °C, with stirring
for 2 h. The mixture was cooled, the reaction was quenched with water and the mixture
was extracted with EtOAc. The organic layers were combined, dried over MgSO4 , filtered and concentrated under reduced pressure to give a residue that was purified
by preparative TLC (SiO2 ) to obtain O -fluoroalkylisourea 4 .
2,2,2-Trifluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4a)
2,2,2-Trifluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4a)
Yield: 42 mg (65%); colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.18 (d, J = 7.1 Hz, 2 H), 7.08 (d, J = 7.3 Hz, 2 H), 7.98 (d, J = 7.4 Hz, 2 H), 7.87 (d, J = 7.2 Hz, 2 H), 5.90 (br, NH), 4.76 (q, J = 8.6 Hz, 2 H), 2.39–2.27 (m, 6 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.66, 143.98, 134.98, 133.49, 132.88, 130.41, 129.48, 122.16, 123.40 (q,
J = 277.2 Hz), 121.12, 62.52 (q, J = 36.4 Hz), 20.76, 20.68.
IR: 3405.37, 2923.81, 1672.99, 1610.85, 1509.22, 1358.83, 1270.01, 1165.46, 1101.68,
820.81 cm–1 .
HRMS (ESI): m /z [M–H]– calcd for C17 H16 F3 N2 O: 321.1220; found: 321.1221.
2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4b)
2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4b)
Yield: 40 mg (65%) from phenylcyanamide and di(p -tolyl)iodonium triflate; 41 mg (67%) from p -tolylcyanamide with diphenyliodonium triflate; colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 6.81–7.36 (m, 9 H), 5.93–5.97 (m, NH), 4.79 (q, J = 8.5 Hz, 2 H), 2.33 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.33, 129.84, 128.98, 124.46, 123.75, 123.38 (q, J = 277.7 Hz), 122.99, 122.34, 121.55, 120.84, 119.13, 117.88, 62.60 (q, J = 36.3 Hz), 21.34.
IR: 3403.27, 2964.35, 2925.31, 1674.50, 1592.52, 1497.72, 1413.23, 1362.41, 1270.90,
1167.92, 1107.64, 766.34, 697.09 cm–1 .
HRMS (ESI): m /z [M–H]– calcd for C16 H14 F3 N2 O: 307.1064; found: 307.1062.
2,2,2-Trifluoroethyl N ′-Phenyl-N -(m -tolyl)carbamimidate (4c)
2,2,2-Trifluoroethyl N ′-Phenyl-N -(m -tolyl)carbamimidate (4c)
Yield: 39 mg (63%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.28–7.36 (m, 2 H), 6.81–7.17 (m, 7 H), 5.92–5.97 (m, NH), 4.79 (q, J = 8.5 Hz, 2 H), 2.33 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.32, 146.55, 139.78, 138.89, 137.54, 137.39, 129.82, 129.64, 128.98, 124.46,
123.73, 123. 58, 123.39 (q, J = 279.6 Hz), 123.03, 122.35, 121.55, 120.84, 119.18, 117.88, 62.60 (q, J = 36.3 Hz), 21.34.
IR: 3407.99, 2925.75, 1673.74, 1592.44, 1362.03, 1270.35, 1107.32, 696.42 cm–1 .
HRMS (ESI): m /z [M–H]– calcd for C16 H14 F3 N2 O: 307.1064; found: 307.1064.
2,2,2-Trifluoroethyl N ′-Phenyl-N -(o -tolyl)carbamimidate (4d)
2,2,2-Trifluoroethyl N ′-Phenyl-N -(o -tolyl)carbamimidate (4d)
Yield: 47 mg (76%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 6.93–7.42 (m, 9 H), 5.80–5.86 (m, NH), 4.82–4.90 (m, 2 H), 2.16–2.26 (m, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 147.76, 144.78, 137.48, 128.97, 123.83, 123.71, 123.36 (q, J = 277.4 Hz), 122.31, 121.98, 120.94, 119.20, 62.43 (q, J = 36.4 Hz), 17.67.
IR: 3450.15, 2925.72, 1674.72, 1595.07, 1498.11, 1361.69, 1270.72, 1166.90, 1103.05,
747.11 cm–1 .
HRMS (ESI): m /z [M + H]+ calcd for C16 H16 F3 N2 O: 309.1209; found: 309.1208.
2,2,2-Trifluoroethyl N -(2-Fluorophenyl)-N ′-phenylcarbamimidatez (4e)
2,2,2-Trifluoroethyl N -(2-Fluorophenyl)-N ′-phenylcarbamimidatez (4e)
Yield: 39 mg (60%); pale-yellow oil.
1 H NMR (400 MHz, CDCl3 ): δ = 6.97–7.46 (m, 8 H), 6.19 (br, 0.35 H), 5.82 (br, 0.59 H), 4.78 (q, J = 8.4 Hz, 2 H), 2.32 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 149.23, 134.54, 134.18, 130.53, 129.55, 124.98, 124.45, 123.38 (q, J = 276.7 Hz), 122.95, 121.92, 116.68, 116.48, 115.30, 62.86 (q, J = 36.5 Hz), 20.80.
IR: 3411.56, 2925.80, 1674.91, 1610.99, 1513.44, 1415.46, 1363.78, 1272.02, 1167.65,
1103.94, 982.73, 753.19 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C16 H13 F4 N2 O: 325.0969; found: 325.0971.
2,2,2-Trifluoroethyl N -(4-Methoxyphenyl)-N ′-phenylcarbamimidate (4f)
2,2,2-Trifluoroethyl N -(4-Methoxyphenyl)-N ′-phenylcarbamimidate (4f)
Yield: 41 mg (63%); pale-yellow waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.26–7.36 (m, 2 H), 6.83–6.70 (m, 7 H), 5.83–5.97 (m, NH), 4.46 (q, J = 7.6 Hz, 2 H), 3.79 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 156.57, 155.99, 148.8, 146.79, 139.46, 137.60, 130.35, 129.79, 128.99, 123.61,
123.44, 123.37 (q, J = 278.0 Hz), 123.15, 122.42, 121.99, 120.72, 115.16, 114.11, 62.52 (q, J = 36.6 Hz), 55.42.
IR: 3403.48, 2931.00, 1670.85, 1512.07, 1362.57, 1269.39, 1238.63, 1164.61, 1101.75,
833.63 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C16 H14 F3 N2 O2 : 323.1013, found: 323.1016.
2,2,2-Trifluoroethyl N -Naphthalen-1-yl-N ′-(p -tolyl)carbamimidate (4g)
2,2,2-Trifluoroethyl N -Naphthalen-1-yl-N ′-(p -tolyl)carbamimidate (4g)
Yield: 64 mg (89%) colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 8.09 (d, J = 7.5 Hz, 1 H), 7.90 (d, J = 7.5 Hz, 1 H), 7.66 (d, J = 8.2 Hz, 1 H), 7.47–7.54 (m, 3 H), 7.07–7.11 (m, 3 H), 6.95 (d, J = 7.8 Hz, 2 H), 5.94 (br, NH), 5.02 (q, J = 8.3 Hz, 2 H), 2.32 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.56, 142.95, 134.75, 134.68, 133.74, 129.44, 128.09, 128.04, 126.39, 126.28,
125.69, 123.59, 123.44 (q, J = 277.7 Hz), 123.39, 121.43, 117.03, 62.56 (q, J = 36.1 Hz), 20.65.
IR: 3397.33, 3054.40, 1669.56, 1515.93, 1362.69, 1271.04, 1165.09, 972.13, 775.92 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C20 H17 F3 N2 O: 357.1220; found: 357.1217.
2,2,2-Trifluoroethyl N -Benzyl-N ′-phenylcarbamimidate (4h)
2,2,2-Trifluoroethyl N -Benzyl-N ′-phenylcarbamimidate (4h)
Yield: 15 mg (24%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.21–7.35 (m, 7 H), 7.03 (t, J = 7.3 Hz, 1 H), 6.88 (d, J = 7.6 Hz, 2 H), 4.68 (q, J = 8.5 Hz, 2 H), 4.44 (br, NH), 4.33 (s, 2 H).
13 C NMR (101 MHz, CDCl3 ): δ = 150.94, 147.19, 138.63, 129.68, 128.64, 127.46, 127.26, 123.43 (q, J = 276.0 Hz), 123.07, 122.48, 122.05, 119.33, 62.47 (q, J = 36.2 Hz), 45.68.
IR: 3423.05, 2926.02, 1671.45, 1593.31, 1413.82, 1269.32, 1164.93, 1120.28, 698.07 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C16 H14 F3 N2 O: 307.1064; found: 307.1067.
2,2,2-Trifluoroethyl N -Cyclohexyl-N ′-phenylcarbamimidate (4i)
2,2,2-Trifluoroethyl N -Cyclohexyl-N ′-phenylcarbamimidate (4i)
Yield: 12 mg (20%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.23–7.30 (m, 2 H), 7.00 (t, J = 7.3 Hz, 1 H), 6.84 (d, J = 7.1 Hz, 2 H), 4.80–4.52 (m, 2 H), 3.88 (br, NH), 3.42 (s, 1 H), 1.85 (d, J = 11.0 Hz, 2 H), 1.53–1.65 (m, 3 H), 1.23–1.29 (m, 3 H), 0.98–1.08 (m, 2 H).
13 C NMR (101 MHz, CDCl3 ): δ = 151.13, 147.59, 129.63, 123. 55 (q, J = 276.7 Hz), 122.82, 122.51, 62.27 (q, J = 35.9 Hz), 50.58, 33.77, 25.40, 24.73.
IR: 3420.90, 2931.61, 2855.92, 1669.28, 1269.72, 1166.65, 762.41 cm–1 .
HRMS (ESI): m /z [M + H]+ calcd for C15 H20 F3 N2 O: 301.1522; found: 301.1519.
2,2,2-Trifluoroethyl N -(4-Chlorophenyl)-N ′-(p -tolyl)carbamimidate (4k)
2,2,2-Trifluoroethyl N -(4-Chlorophenyl)-N ′-(p -tolyl)carbamimidate (4k)
Yield: 42 mg (62%); colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 6.78–7.42 (m, 8 H), 5.81–5.93 (m, NH), 4.75 (q, J = 8.2 Hz, 1.83 H), 4.56 (q, J = 8.0 Hz, 0.13 H), 2.32 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.81, 145.28, 130.48, 129.84, 129.54, 129.98, 123.77, 123.29 (q, J = 277.4 Hz), 122.02, 121.38, 62.63 (q, J = 36.5 Hz), 20.70.
IR: 3404.79, 2925.49, 1672.80, 1492.03, 1360.44, 1270.70, 1167.44, 1096.49, 824.27 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C14 H13 ClF3 N2 O: 341.0674; found: 341.0671.
2,2,2-Trifluoroethyl N ′-(4-Bromophenyl)-N -(p -tolyl)carbamimidate (4l)
2,2,2-Trifluoroethyl N ′-(4-Bromophenyl)-N -(p -tolyl)carbamimidate (4l)
Yield: 27 mg (35%); colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.39–7.45 (m, 2 H), 6.71–7.20 (m, 6 H), 5.80–5.92 (m, NH), 4.75 (q, J = 8.3 Hz, 1.79 H), 4.55 (q, J = 8.2 Hz, 0.11 H), 2.31 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.66, 132.79, 131.93, 130.41, 129.55, 124.23, 123.24 (q, J = 279.0 Hz), 122.32, 121.91, 121.41, 116.34, 62.66 (q, J = 36.4 Hz), 20.74.
IR: 3407.63, 2924.93, 1672.11, 1513.56, 1488.70, 1359.04, 1269.88, 1166.53, 821.60 cm–1 .
HRMS (ESI): m /z [M + H]+ calcd for C14 H15 BrF3 N2 O: 387.0314; found: 387.0317.
2,2,2-Trifluoroethyl N ′-(4-(tert -Butyl)phenyl)-N -(p -tolyl)carbamimidate (4m)
2,2,2-Trifluoroethyl N ′-(4-(tert -Butyl)phenyl)-N -(p -tolyl)carbamimidate (4m)
Yield: 40 mg (55%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.30–7.37 (m, 2 H), 7.08–7.16 (m, 2 H), 6.87–6.98 (m, 4 H), 5.93 (br, NH),
4.77 (q, J = 8.0 Hz, 2 H), 2.31–2.34 (m, 3 H), 1.32 (s, 9 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.56, 130.40, 129.48, 126.67, 125.84, 122.15, 121.84, 121.26, 120.31, 62.51
(q, J = 35.9 Hz), 34.26, 31.38, 20.74.
IR: 3405.39, 2962.96, 1673.61, 1609.49, 1513.14, 1361.23, 1270.55, 1166.57, 1103.66,
824.92 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C20 H22 F3 N2 O: 363.1690; found: 363.1693.
2,2,2-Trifluoroethyl N ′-(2,5-Dimethylphenyl)-N -(p -tolyl)carbamimidate (4n)
2,2,2-Trifluoroethyl N ′-(2,5-Dimethylphenyl)-N -(p -tolyl)carbamimidate (4n)
Yield: 51 mg (76%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 6.73–7.15 (m, 7 H), 5.75 (br, NH), 4.81–4.87 (m, 2 H), 2.33 (s, 3 H), 3.32
(s, 3 H), 2.08–2.17 (m, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 147.70, 144.76, 136.92, 135.0, 133.64, 130.95, 130.43, 129.54, 127.34, 124.41,
122.47, 122.14, 121.38, 62.39 (q, J = 36.4 Hz), 21.02, 20.74, 17.27.
IR: 3408.34, 2924.07, 1673.26, 1611.24, 1514.20, 1358.85, 1270.39, 1166.19, 811.07 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C18 H18 F3 N2 O: 335.1377; found: 335.1378.
2,2,2-Trifluoroethyl N ′-Mesityl-N -(p -tolyl)carbamimidate (4o)
2,2,2-Trifluoroethyl N ′-Mesityl-N -(p -tolyl)carbamimidate (4o)
Yield: 51 mg (73%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.07–7.17 (m, 2 H), 6.85–6.96 (m, 4 H), 5.57 (br, 0.74 H), 5.32 (br, 0.23 H),
4.89 (q, J = 8.4 Hz, 1.52 H), 4.70 (q, J = 8.1 Hz, 0.44 H), 2.29–2.34 (m, 6 H), 2.14–2.18 (m, 6 H).
13 C NMR (101 MHz, CDCl3 ): δ = 147.01, 140.48, 134.91, 133.58, 132.53, 129.54, 129.20, 127.56, 124.80, 123.42
(q, J = 278.6 Hz), 122.26, 121.44, 119.28, 62.20 (q, J = 36.4 Hz), 20.68, 20.66, 17.97, 17.80.
IR: 3396.09, 2922.11, 1675.51, 1611.58, 1514.45, 1357.22, 1271.30, 1167.24, 1104.41,
981.66, 820.59 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C19 H20 F3 N2 O: 349.1533; found: 349.1535.
2,2,2-Trifluoroethyl N ′-(4-(tert -Butyl)phenyl)-N -(p -tolyl)carbamimidate / 2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4m/4m′)
2,2,2-Trifluoroethyl N ′-(4-(tert -Butyl)phenyl)-N -(p -tolyl)carbamimidate / 2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4m/4m′)
Yield: 44 mg (64%); 4m /4m′ =1.5:1; pale-yellow oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.30–7.34 (m, 2.95 H), 7.89–7.17 (m, 10.23 H), 5.94 (br, 1.54 H), 4.78 (m,
3.12 H), 2.33 (br, 5.42 H), 1.33 (s, 9 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.54, 143.83, 134.99, 129.83, 128.98, 125.83, 124.76, 122.40, 122.05, 121.24,
120.29, 62.57 (q, J = 36.4 Hz), 62.51 (q, J = 36.4 Hz), 34.25, 31.36, 20.73.
IR: 3404.90, 2963.49, 2928.48, 1674.19, 1607.41, 1513.58, 1414.69, 1362.44, 1270.97,
1167.46, 1104.34, 981.13, 825.09 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C16 H14 F3 N2 O: 307.1064; found: 307.1067; m /z [M – H]– calcd for C20 H22 F3 N2 O: 363.1690; found: 363.1693.
2,2,2-Trifluoroethyl N ′-(4-Iodophenyl)-N -(p -tolyl)carbamimidate / 2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4p/4p′)
2,2,2-Trifluoroethyl N ′-(4-Iodophenyl)-N -(p -tolyl)carbamimidate / 2,2,2-Trifluoroethyl N -Phenyl-N ′-(p -tolyl)carbamimidate (4p/4p′)
Yield: 45 mg (61%); 4p /4p′ =1:1.1; pale-yellow oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.57–7.64 (m, 0.88 H), 7.28–7.36 (m, 0.95 H), 7.67–7.15 (m, 6.39 H), 5.80–5.94
(m, 1 H), 4.72–4.80 (m, 2 H), 2.32 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 148.59, 146.53, 138.82, 137.97, 130.47, 129.86, 129.59, 129.03, 124.82, 123.58,
122.06, 121.92, 121.46, 121.29, 120.82, 86.90, 62.68 (q, J = 36.0 Hz), 62.64 (q, J = 36.3 Hz), 20.79.
IR: 3404.56, 3026.19, 2925.05, 2856.81, 1673.06, 1593.32, 1514.54, 1492.04, 1414.79,
1361.07, 1270.28, 1166.97, 1102.15, 980.08, 812.92 cm–1 .
HRMS (ESI): m /z [M + H]+ calcd for C16 H16 F3 N2 O: 309.1209; found: 309.1207; m /z [M – H]– calcd for C16 H14 F3 IN2 O: 433.0030; found: 433.0031.
2-Fluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4r)
2-Fluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4r)
Yield: 28 mg (49%); colourless oil.
1 H NMR (400 MHz, CDCl3 ): δ = 7.64 (d, J = 8.2 Hz, 2 H), 7.19 (d, J = 8.1 Hz, 2 H), 7.09 (d, J = 7.9 Hz, 2 H), 7.00 (d, J = 7.9 Hz, 2 H), 4.41 (t, J = 7.5 Hz, 2 H), 3.99 (t, J = 7.5 Hz, 2 H), 2.35 (s, 3 H), 2.32 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 149.26, 144.84, 137.22, 132.45, 131.55, 129.28, 129.09, 122.94, 118.92, 63.60,
46.5, 20.79, 20.68.
IR: 3425.30, 2920.65, 1673.61, 1606.30, 1508.24, 1400.43, 1312.80, 1201.39, 1101.60,
1041.78, 809.95 cm–1 .
HRMS (ESI): no molecular ion peak was found.
2,2-Difluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4s)
2,2-Difluoroethyl N ,N ′-Di-p -tolylcarbamimidate (4s)
Yield: 52 mg with di(p -tolylcyanamide) (63%); pale-yellow waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.11–7.28 (m, 8 H), 6.22 (tt, J = 55.5, 3.9 Hz, 1 H), 5.95 (br, NH), 4.60 (td, J = 13.6, 3.9 Hz, 2 H), 2.40 (s, 3 H), 2.37 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 149.24, 144.25, 135.18, 133.30, 132.66, 129.41, 122.22, 115.42, 113.03 (t,
J = 240.9 Hz), 110.64, 64.55 (t, J = 29.9 Hz), 20.72, 20.67.
IR: 3707.84, 2922.41, 1662.54, 1506.18, 1084.39, 809.14 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C17 H17 F2 N2 O: 303.1314; found: 303.1315.
1,1,1,3,3,3-Hexafluoropropan-2-yl N ,N ′-Di-p -tolylcarbamimidate (4t)
1,1,1,3,3,3-Hexafluoropropan-2-yl N ,N ′-Di-p -tolylcarbamimidate (4t)
Yield: 40 mg (51%); pale-yellow waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.18 (d, J = 7.6 Hz, 2 H), 7.09 (d, J = 7.6 Hz, 2 H), 6.94 (d, J = 31.8, 7.9 Hz, 2 H), 6.86 (d, J = 31.8, 7.9 Hz, 2 H), 6.56 (hept, J = 12.8, 6.3 Hz, 1 H), 5.94 (br, NH), 2.35 (s, 3 H), 2.31 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 147.30, 142.93, 134.32, 134.17, 133.36, 130.45, 129.58, 121.94, 121.90, 120.92
(q, J = 280.1 Hz), 67.85 (hept, J = 34.2 Hz), 20.79, 20.72.
IR: 3402.97, 2926.74, 1684.92, 1611.36, 1512.87, 1357.28, 1276.98, 1230.50, 1195.80,
1108.88, 821.78 cm–1 .
HRMS (ESI): m /z [M + H]+ calcd for C18 H17 F6 N2 O: 391.1240; found: 391.1239.
Ethyl N ,N ′-Di-p -tolylcarbamimidate (4u)
Ethyl N ,N ′-Di-p -tolylcarbamimidate (4u)
Yield: 18 mg (34%); colourless waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.19–7.01 (m, 4 H), 6.88–6.94 (m, 4 H), 5.80 (br, NH), 4.40 (q, J = 7.0 Hz, 2 H), 2.31 (s, 6 H), 1.40 (t, J = 7.1 Hz, 3 H).
13 CNMR (101 MHz, CDCl3 ): δ = 150.36, 136.07, 132.53, 132.12, 130.25, 129.85, 129.32, 122.52, 120.61, 62.57,
20.74, 20.66, 14.32.
IR: 3412.51, 1657.62, 1610.38, 1510.33, 1381.07, 1327.68, 1232.22, 1064.68, 813.77 cm–1 .
HRMS (ESI): m /z [M – H]– calcd for C17 H19 N2 O: 267.1503; found: 267.1504.
Synthesis of 2-Fluoroalkoxybenzimidazoles through PhI(OAc)2 -Promoted C–H Activation of O -Fluoroalkyl Isoureas; General Procedure
Synthesis of 2-Fluoroalkoxybenzimidazoles through PhI(OAc)2 -Promoted C–H Activation of O -Fluoroalkyl Isoureas; General Procedure
To a round-bottom flask, O -fluoroalkylisourea 4 (0.2 mmol, 1.0 equiv), PhI(OAc)2 (0.4 mmol, 2 equiv) and acetonitrile (3 mL) were added and the mixture was stirred
at r.t. for 45 min, then concentrated under reduced pressure to give a residue, which
was purified to obtain 2-fluoroalkoxybenzimidazole 5 after preparative TLC (SiO2 ).
6-Methyl-1-(p -tolyl)-2-(2,2,2-trifluoroethoxy)-1H -benzo[d ]imidazole (5a)
6-Methyl-1-(p -tolyl)-2-(2,2,2-trifluoroethoxy)-1H -benzo[d ]imidazole (5a)
Yield: 58 mg (91%); pale-yellow waxy solid.
1 H NMR (400 MHz, CDCl3 ): δ = 7.49 (d, J = 8.1 Hz, 1 H), 7.41–7.30 (m, 4 H), 7.07 (d, J = 8.1 Hz, 1 H), 7.02 (s, 1 H), 4.96 (q, J = 8.2 Hz, 2 H), 2.46 (s, 3 H), 2.42 (s, 3 H).
13 C NMR (101 MHz, CDCl3 ): δ = 154.56, 138.17, 137.05, 134.68, 132.04, 131.45, 130.18, 122.75 (q, J = 277.8 Hz), 125.65, 123.72, 117.70, 109.73, 65.77 (q, J = 37.0 Hz), 21.63, 21.14.
IR: 3446.07, 2962.47, 2924.88, 1630.20, 1547.98, 1517.91, 1442.49, 1273.13, 1169.82,
1091.37, 962.70, 808.55 cm–1 .
HRMS (ESI): no molecular ion peak was found.