Chemistry of phosphorus ylides: Part 44 reaction of 1-trimethylsilyl-1H-imidazole with phosphorus reagents. A convenient synthesis of phosphorus silyl imidazoles

Article abstract of DOI:10.3184/174751916X14597795711995

The reaction of 1-trimethylsilyl-1H-imidazole with nucleophilic active phosphacumulenes afforded imidazole silyl phosphoranylidenes or imidazole phosphoranylidenes according to the reaction conditions. The reaction of hexaphenylcarbodiphosphorane with 1-trimethylsilyl-1H-imidazole resulted in the formation of silyl phosphoranylidene phosphoranyl imidazole, silyl phosphoranylidene imidazole and triphenylphosphane. Moreover, Lawesson and Japanese reagents afforded imidazole phosphinothioic thioanhydrides.

Full text of DOI:10.3184/174751916X14597795711995

JOURNAL OF CHEMICAL RESEARCH 2016
VOL. 40 MAY, 265–268
RESEARCH PAPER 265
Chemistry of phosphorus ylides: Part 44
Reaction of 1-trimethylsilyl-1H-imidazole with phosphorus reagents.
A convenient synthesis of phosphorus silyl imidazoles
Marwa El-Hussieny, Mansoura Ali Abd-El-Maksoud, Soher Said Maigali and
Fouad Mohamed Soliman*
Department of Organometallic and Organometalloid Chemistry, National Research Centre, 33 El-Bohouth St. (former El Tahrir St.), Dokki, Giza 12622, Egypt
The reaction of 1-trimethylsilyl-1H-imidazole with nucleophilic active phosphacumulenes afforded imidazole silyl phosphoranylidenes or
imidazole phosphoranylidenes according to the reaction conditions. The reaction of hexaphenylcarbodiphosphorane with 1-trimethylsilyl-
1H-imidazole resulted in the formation of silyl phosphoranylidene phosphoranyl imidazole, silyl phosphoranylidene imidazole and
triphenylphosphane. Moreover, Lawesson and Japanese reagents afforded imidazole phosphinothioic thioanhydrides.
Keywords: 1-trimethylsilyl-1H-imidazole, phosphonium ylides, Lawesson’s reagent, phosphoranylidenes, phosphinothioic thioanhydride
Trimethylsilylimidazoles have received much attention because
of their synthetic and application challenges.1,2 Moreover, the
trimethylsilyl group is characterised by chemical inertness and
a large molecular volume, which makes it useful in a number
of applications.3–5 Trimethylsilylimidazoles are used as silyl
protecting and derivatisation reagents,6,7 reducing agents,8 in
cross-coupling chemistry9 and to stabilise α-carbanions and
β-carbocations.9
Previously we studied the reactions of the active
phosphacumulenes, phosphallenes, stabilised phosphonium
ylides, Lawesson and Japanese reagents to prepare new
heterocyclic and homocyclic compounds containing phosphorus
moieties of industrial and biological interest.10–19
of the trimethylsilyl group between N and phosphorane C,
when the reaction was performed in dry toluene. Subsequently,
a desilylation reaction of compound 3a occurred with the
formation of 4a and trimethylsilanol when the reaction was
carried out in THF and the product chromatographed on silica
gel. The structures of compounds 3a and 4a were elucidated
1
by H, 13C and 31P NMR spectroscopy and mass spectrometry.
The most important features in their NMR spectra are the
appearance of the trimethylsilyl group at δ –0.026 and 16.11 in
1
the H NMR and 13C NMR of compound 3a respectively and
their absence in compound 4a. Also a doublet appeared at δ 3.18
(2JH-P = 21), assigned to H–C=P(Ph)3, in the 1H NMR spectrum
of 4a. When 1 reacted with the active (2-oxovinylidene)
triphenylphosphorane (2b) in dry boiling toluene, the
corresponding imidazolesilanylphosphoranylidene ethanone
3b was isolated. In addition, the reaction of 1 with 2b in THF
proceeded with the formation of imidazolephosphoranylidene
ethanone 4b. (Scheme 1).
Results and discussion
We now report the reaction of 1-trimethylsilyl-1H-imidazole
(1) with (N-phenyliminovinylidene)triphenylphosphorane (2a),
(2-oxovinylidene)triphenylphosphorane (2b), hexaphenylcarbo-
diphosphorane (5), Lawesson’s reagent (8a) and Japanese reagent
9a (Schemes 1–4). The phosphacumulene ylides (2a and 2b)
can each be described by the resonance structures 2A and 2B
(Scheme 1). Accordingly, treatment of 1 with 1 equiv. of 2a in dry
toluene led to the formation of imidazolesilylphosphoranylidene
aniline 3a. When the reaction was performed in hot THF and the
product was chromatographed on silica gel, the new compound
imidazolephosphoranylidene aniline 4a was isolated. Adduct 3a
was formed by nucleophilic attack of 2a on 1 and fast exchange
The
reaction
of
1
with
the
phosphallene,
hexaphenylcarbodiphosphorane (5), was also investigated.
Compounds 1 and 5 react in equimolar ratio in boiling toluene
to give two products, silylphosphoranylidenephosphoranyl
imidazole 6 and silylphosphoranylidene imidazole 7, together
with triphenylphosphane. The reaction proceeds by nucleophilic
reaction of compound 5 on 1, producing compound 6. Since
triphenylphosphane is a good leaving group, fragmentation and
rearrangement of 6 occurs with the formation of compound 7
(Ph)3P
C
C
X
(2B)
N
N
H
2O
N
+
+
HO Si(CH3)3
(Ph)3P
C
C
X
(2A)
H
N
C
N
N
C
Si(CH3)3
P(Ph)3
X
C
X
C
Si(CH3)3
P(Ph)3
2a, X = NPh
b, X = O
4a, X = NPh
b, X = O
1
3a, X = NPh
b, X = O
Scheme 1
* Correspondent. E-mail: solimanfma2@yahoo.com

266 JOURNAL OF CHEMICAL RESEARCH 2016
and triphenylphosphane. In the 31P NMR spectrum of compound
6, two signals were observed at δ 23.20 and 29.04 ppm, while
compound 7 showed only one signal at δ 20.45 ppm (Scheme 2).
It is well-known that Lawesson’s reagent, 2,4-bis(4-
In addition, the reaction of 1 with diphenyl hydrogen
phosphate (16) was performed in boiling THF and diphenyl
1H-imidazol-1-ylphosphonate (17) was obtained, along with
trimethylsilanol. The 31P NMR spectrum of 17 showed a signal
at δ –11.00 ppm and the mass spectrum showed an ion peak at
m/z 301 [M + H]+ (Scheme 4).
methoxyphenyl)-1,3,2,4-dithiaphosphetane-2,4-disulfide
(8a)
can be in equilibrium with a highly reactive thiophosphine
ylide (8b ↔ 8c). Compound 8b ↔ 8c which is depicted in
Scheme 3,20 can react with 1 in boiling toluene for 5 h to give
an imidazole phosphinothioic thioanhydride 14. When 1 reacted
with 2,4-bisthiophenyl-1,3,2,4-dithiaphosphetane-2,4-disulfide
(9a) in boiling toluene for 7 h, the corresponding imidazole
phosphinothioic thioanhydride 15 was obtained. It is believed that
8b or 9b reacted first with 1 to form the intermediate 10 or 11,
which decomposed to the dithiol 12 or 13 and trimethylsilanol.
Expulsion of hydrogen sulfide from two moles afforded the final
products 14 or 15. A signal at δ 93.28 ppm was observed in the 31P
NMR spectrum of compound 15 (Scheme 3).
Conclusion
From the above results, the reaction of 1-trimethylsilyl-1H-
imidazole (1) with active phosphacumulenes represents an
interesting approach to the synthesis of phosphorus substances,
coupled with desilylation due to the high nucleophilicity of
phosphacumulene reagents. In contrast, the reaction with
phosphallene ylide, which is less nucleophilic, afforded the
silylated phosphorus compounds. The reaction of the Lawesson
and Japanese reagents with 1 resulted in desilylation coupled with
the formation of new compounds containing phosphorus and
N
N
N
Ph3P
C
PPh3
+
+ P(Ph)3
N
N
C
N
(H3C)3Si
P(Ph)3
Si(CH3)3
(H3C)3Si
P(Ph)3
C
5
7
P(Ph)3
1
6
Scheme 2
S
S
S
S
2
P
Ar
P
Ar
P
S
Ar
Ar
P
S
S
S
8c, Ar = -C6H4-OCH3
9c, Ar = -S-C6H5
8b, Ar = -C6H4-OCH3
9b, Ar = -S-C6H5
8a, Ar = -C6H4-OCH3
9a, Ar = -S-C6H5
N
N
N
S
H
2O
+
+
P
S
Ar
(CH3)3SiOH
N
S
P
S
N
N
P
H
S
S
Ar
8b, Ar = -C6H4-OCH3
9b, Ar = -S-C6H5
Si(CH3)3
Si(CH3)3
Ar
1
12, Ar = -C6H4-OCH3
13, Ar = -S-C6H5
10, Ar = -C6H4-OCH3
11, Ar = -S-C6H5
N
N
-H2S
N
N
P
P
S
S
S
Ar
Ar
14, Ar = -C6H4-OCH3
15, Ar = -S-C6H5
Scheme 3

JOURNAL OF CHEMICAL RESEARCH 2016 267
N
N
C6H5
O
+
O
C6H5
P
+
(CH3)3SiOH
N
N
P
O
HO
C6H5
O
O
C6H5
16
Si(CH3)3
O
1
17
Scheme 4
triphenylphosphorane (2b) (0.30 g, 0.001 mol) with 1 was performed in
THF, the reaction mixture was refluxed for 5 h when using 2a and for
6 h when using 2b. THF was distilled off under reduced pressure and
the residue was subjected to silica gel column chromatography using
petroleum ether (60–80 °C)/acetone to give 4a or 4b together with
trimethylsilanol.
sulfur moieties. On the other hand, the reaction of 1 with diphenyl
hydrogen phosphate (16) resulted in desilylation and formation
of a new imidazole phosphonate. It is evident that this synthetic
strategy has opened multifaceted preparative possibilities.
Experimental
N-[1- (1H-Imidazol-1-yl) -2- (triphenylphosphoranylidene)
ethylidene]aniline (4a): Eluent: petroleum ether (60–80 °C)/
acetone (3:7, v/v); colourless crystals; yield 35%; m.p. 277 °C; IR
Melting points were determined with an electrothermal digital melting
point apparatus (Electro-Thermal Engineering Ltd., Essex, UK).
The IR spectra were recorded in KBr disks on Pye Unicam SP 3300
1
(KBr) (ν cm–1): 1626 (Ph–N=C), 1433 (C=P); H NMR (500 MHz,
1
and Shimadzu FT IR 8101 PC instruments. H and 13C NMR spectra
DMSO-d6, δppm): 3.18 (d, 1H, H-C=P(Ph)3), 6.90–7.75 (m, 23H, arom.);
13C NMR (500 MHz, DMSO-d6, δppm): 122.46–150.28 (C–arom.),
151.29 (C=P), 166.70 (C=N); 31P NMR (202.4 MHz, CDCl3, δ ppm):
26.16; MS m/z: 445 M+. Anal. calcd for C29H24N3P (445.49): C, 78.19;
H, 5.43; N, 9.43; P, 6.95; found: C, 78.10; H, 5.42; N, 9.39; P, 6.86%.
1-(1H-Imidazol-1-yl)-2-(triphenylphosphoranylidene)ethanone
(4b): Eluent: petroleum ether (60–80 °C)/acetone (4:6, v/v); colourless
were obtained with a Jeol ECA 500 MHz NMR spectrometer using
deuterated dimethylsulphoxide (DMSO-d6) as a solvent and TMS as an
internal reference at 500 and 125 MHz respectively. 31P NMR spectra
were obtained at 200 MHz. Mass spectra (EI-MS) were obtained
with an ISQ (Single Quadrupole MS, Thermo Scientific) instrument.
Elemental analyses (C, H, N) were obtained with an Elementar Vario
EL instrument and phosphorus was measured by spectrophotometric
methods. Silicon was measured using micro-sample volume introduction
into an atomic absorption spectrometer (Agilent technology 200
series AA). All data agreed satisfactory with the calculated values.
The recorded yields are of pure isolated materials obtained by
column chromatography using silica gel 60 (Merck) and thin layer
chromatography (TLC), which was performed on Merck Kiesel gel F254
pre-coated plates. Solvents were dried/purified according to literature
procedures. The starting material 1 was obtained from Aldrich.
1
crystals; yield 30%; m.p. 110 °C; H NMR (500 MHz, DMSO-d6,
δ
ppm): 2.06 (d, 1H, H–C=P(Ph)3), 7.47–7.76 (m, 18H, arom.); 13C NMR
(500 MHz, DMSO-d6, δppm): 115.12–146.69 (C–arom.); 153.53 (C=P);
184.33 (C=O); 31P NMR (202.4 MHz, DMSO-d6, δppm): 27.07. Anal.
calcd for C23H19N2OP (370.38): C, 74.58; H, 5.17; N, 7.56; P, 8.36;
found: C, 74.50; H, 5.12; N, 7.52; P, 8.31%.
Reaction of hexaphenylcarbodiphosphorane (5) with 1-trimethylsilyl-
1H-imidazole (1)
A
mixture of 1-trimethylsilyl-1H-imidazole (1) (0.14 g,
Reaction of 1-trimethylsilyl-1H-imidazole (1) with active
phosphacumulene ylides 2a and 2b
0.001 mol) in 20 mL of dry toluene was added dropwise to a solution of
hexaphenylcarbodiphosphorane23 (5) (0.53 g, 0.001 mol) in 20 mL of dry
toluene. The reaction mixture was refluxed for 10 h until no more of the
starting materials could be detected (TLC). Toluene was distilled off
under reduced pressure and the remaining residue was chromatographed
on silica gel using petroleum ether (60–80 °C)/ethyl acetate as an eluent
to form compounds 6 and 7 together with triphenylphosphane.
A solution of 1-trimethylsilyl-1H-imidazole (1) (0.14 g, 0.001 mol) in dry
toluene (20 mL) was added to a solution of (N-phenyliminovinylidene)
triphenylphosphorane (2a)21 (0.37 g, 0.001 mol) or (2-oxovinylidene)
triphenylphosphorane (2b)22 (0.30 g, 0.001 mol) in toluene (20 mL). The
reaction mixture was refluxed for 5 h when using 2a and for 7 h when
using 2b. The solvent was removed under reduced pressure and the
residue was crystallised from ethyl acetate/petroleum ether (60–80 °C)
to give 3a or 3b.
N - [ 1 - ( 1 H - I m i d a z o l - 1 - y l ) - 2 - ( t r i m e t h y l s i l y l ) - 2 -
(triphenylphosphoranylidene)ethylidene]aniline (3a): Yellow crystals;
yield 55%; m.p. 164 °C; IR (KBr) (ν cm–1): 1626 (C=NPh), 1427 (C=P);
1H NMR (500 MHz, DMSO-d6, δppm): –0.026 (s, 9H, Si(CH3)3), 6.87–8.40
(m, 23H, arom.); 13C NMR (500 MHz, DMSO-d6, δppm): 16.11 (3CH3),
117.03–136.80 (C–arom.), 148.00, 151.31 (2C=N); 31P NMR (202.4 MHz,
DMSO-d6, δppm): 20.67; MS m/z: 517 M+. Anal. calcd for C32H32N3PSi
(517.68): C, 74.24; H, 6.23; N, 8.12; P, 5.98; Si, 5.43; found: C, 74.18; H,
6.15; N, 8.00; P, 5.90; Si, 5.38%.
1- (1H-Imidazol-1-yl) -2- (trimethylsilyl) -2- (triphenyl-
phosphoranylidene)ethanone (3b): Eluent: petroleum ether 60–80 °C/
ethyl acetate (2:8, v/v); colourless crystals; yield 65%; m.p. 100 °C;
IR (KBr) (ν cm–1): 1628 (br, C=O), 1431 (C=P); 1H NMR (500 MHz,
DMSO-d6, δppm): –0.0024 (s, 9H, Si(CH3)3), 7.70–8.19 (m, 18H, arom.);
31P (202.4 MHz, DMSO-d6, δppm): 20.40 MS m/z: 441 [M – H]+. Anal.
calcd for C26H27N2OPSi (442.56): C, 70.56; H, 6.15; N, 6.33; P, 7.00; Si,
6.35; found: C, 70.50; H, 6.05; N, 6.21; P, 6.98; Si, 6.29%.
1-{Triphenyl[(trimethylsilyl)(triphenylphosphoranylidene)methyl]
phosphoranyl}-1H-imidazole (6): Eluent: petroleum ether (60–80 °C)/
ethyl acetate (6:4, v/v) as: Colourless crystals; m.p. 136 °C; yield 25%;
IR (KBr) (ν cm–1): 1429 (C=P); 1H NMR (500 MHz, DMSO-d6, δppm):
–0.038 (s, 9H, Si–(CH3)3), 6.77–7.52 (m, 33H, arom.); 31P NMR (202.4
MHz, CDCl3, δppm): 23.20 and 29.04; MS m/z: 414 [M – Ph3P]+, 262
[Ph3P]+. Anal. calcd for C43H42N2P2Si (676.84): C, 76.30; H, 6.25; N,
4.14; P, 9.15; Si, 4.15; found: C, 76.29; H, 6.20; N, 4.10; P, 9.08; Si, 4.10%.
1-[(Trimethylsilyl)(triphenylphosphoranylidene)methyl]-1H-
imidazole (7): Eluent: petroleum ether (60–80 °C)/ethyl acetate (3:7,
v/v); yellow crystals; m.p. 110 °C; yield 30%; IR (KBr) (ν cm–1): 1429
(C=P); 1H NMR (500 MHz, DMSO-d6, δppm): –0.038 (s, 9H, Si–
(CH3)3), 7.43–7.50 (m, 18H, arom.); 31P NMR (202.4 MHz, CDCl3,
δ
ppm): 20.45; MS m/z: 152 [M – Ph3P]+, 262 [Ph3P]+. Anal. calcd for
C25H27N2PSi (414.55): C, 72.43; H, 6.56; N, 6.76; P, 7.47; Si, 6.77;
found: C, 72.39; H, 6.53; N, 6.72; P, 7.42; Si, 6.70%.
Reaction of Lawesson’s reagent (8a) or 4-bisthiophenyl-1,3,2,4-
dithiaphosphetane-2,4-disulfide (9a) with 1-trimethylsilyl-1H-
imidazole (1)
When the reaction of (N-phenyliminovinylidene)triphenyl-
phosphorane (2a) (0.37 g, 0.001 mol) or (2-oxovinylidene)
A solution of 1-trimethylsilyl-1H-imidazole (1) (0.14 g, 0.001 mol) in
dry toluene (20 mL) was added to a solution of Lawesson’s reagent24

268 JOURNAL OF CHEMICAL RESEARCH 2016
(8a) (0.40 g, 0.001 mol) or the Japanese reagent25 9a (0.40 g, 0.001 mol)
in dry toluene (20 mL). The reaction mixture was refluxed for 10 h
when using 8a and for 7 h when using 9a, during which H2S gas was
evolved. The solvent was removed under reduced pressure and the
residue was chromatographed on silica gel using petroleum ether
60–80 °C ethyl acetate as an eluent to give 14 or 15.
(1H-Imidazol-1-yl) (4-methox yphenyl) phosphinothioic
thioanhydride (14): Eluent: petroleum ether (60–80 °C)/ethyl acetate
(3:7, v/v); white crystals; yield 35%, m.p. 175–177 °C; IR (KBr)
(ν cm–1): 2923 (OCH3), 1602 (C=N), 651 (P=S); 1H NMR (500 MHz,
DMSO-d6, δppm): 3.79 (s, 6H, 2OCH3), 6.98–7.74 (m, 14H, arom.);
13C NMR (500 MHz, DMSO-d6, δppm): 55.64 (OCH3), 113.87–133.00
(C–arom.), 161.61 (C–OCH3); MS m/z: 508 [M + 2]+. Anal. calcd
for C20H20N4O2P2S3 (506.54): C, 47.42; H, 3.98; N, 11.06; P, 12.23; S,
18.99; found: C, 47.39; H, 3.95; N, 11.00; P, 12.21; S, 19.00%.
References
1
T.N. Komarova, L.I. Larina, E.V. Abramova and G.V. Dolgushin, Russ. J.
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3
S. Lakhdar, M. Baidya and H. Mayr, Chem. Commun., 2012, 48, 4504.
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K. Dey, Proc. Indian Natn. Sci. Acad., 1989, 55, 243.
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9
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(1H-Imidazol-1-yl)(thiophenyl)phosphinothioic thioanhydride (15):
Eluent: petroleum ether (60–80 °C)/ethyl acetate (4:6, v/v); white
crystals; yield 55%, m.p. 88–91 °C; IR (KBr) (ν cm–1): 1631 (C=N),
686 (P=S); 1H NMR (500 MHz, DMSO-d6, δppm): 7.39–7.56 (m,
16H, arom.); 13C NMR (500 MHz, DMSO-d6, δppm): 122.00–132.50
(C–arom.); 31P NMR (202.4 MHz, DMSO-d6, δppm): 93.28. Anal. calcd
for C18H16N4P2S5 (510.62): C, 42.34; H, 3.16; N, 10.97; P, 12.13; S,
31.40; found: C, 42.30; H, 3.13; N, 10.95; P, 12.11; S, 31.35%.
10 M. El-Hussieny, M.A. Abd-El-Maksoud, S.S. Maigali, F.M. Soliman and
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13 M.A. Abd-El-Maksoud, S.S. Maigali and F.M. Soliman, J. Heterocycl.
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Reaction of diphenyl hydrogen phosphate (16) with 1-trimethylsilyl-
1H-imidazole (1)
A mixture of 1-trimethylsilyl-1H-imidazole (1) (0.14 g, 0.001 mol)
in dry THF (20 mL) was added dropwise to a solution of 16 (0.25 g,
0.001 mol) in dry THF (20 mL). The reaction mixture was refluxed for
8 h until no more of the starting materials could be detected (TLC).
THF was distilled off under reduced pressure and the remaining
residue was chromatographed on silica gel using petroleum ether
(60–80 °C)/ethyl acetate as an eluent (4:6) to form compound 17.
Diphenyl 1H-imidazol-1-ylphosphonate (17): White crystals; yield
50%; m.p. 98–100 °C; IR (KBr) (ν cm–1): 1591 (C=N); 1H NMR (500
MHz, CDCl3, δppm): 6.78–7.56 (m, 13H, arom.); 13C NMR (500 MHz,
DMSO-d6, δppm): 122.00–157.30 (C–arom.); 31P NMR (202.4 MHz,
CDCl3, δppm): –11.00; MS m/z: 301 [M + H]+; Anal. calcd for
C15H13N2O3P (300.25): C, 60.00; H, 4.36; N, 9.33; P, 10.32; found: C,
59.89; H, 4.33; N, 9.30; P, 10.21%.
Received 15 December 2015; accepted 11 February 2016
Paper 1503777 doi: 10.3184/174751916X14597795711995
Published online: 22 April 2016