Metal-free hydrophosphanation of 1-vinylimidazoles with secondary phosphanes: A straightforward atom-economic route to tertiary phosphanes with imidazolyl substituents

Article abstract of DOI:10.1055/s-0030-1259103

Free radical addition (UV irradiation, 2-7 h or AIBN, 65-70 °C, 6-7 h) of secondary phosphanes to 1-vinylimidazole, 2-methyl-1-vinylimidazole, and 1-vinylbenzimidazole proceeds regio-selectively to give the corresponding anti-Markovnikov adducts in 88-98%

Full text of DOI:10.1055/s-0030-1259103

94
LETTER
Metal-Free Hydrophosphanation of 1-Vinylimidazoles with Secondary
Phosphanes: A Straightforward Atom-Economic Route to Tertiary
Phosphanes with Imidazolyl Substituents
H
ydrophosphanat
o
ion of 1-Vin
r
ylimidaz
i
oles
w
s
ith Secondar
y
Ph
A
osphane
s
. Trofimov,* Svetlana F. Malysheva, Lidiya N. Parshina, Nina K. Gusarova, Nataliya A. Belogorlova
A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, 1 Favorsky Str., 664033 Irkutsk, Russia
Fax +7(3952)419346; E-mail: boris_trofimov@irioch.irk.ru
Received 13 October 2010
vinylimidazoles can be considered as a simple, single-step
Abstract: Free radical addition (UV irradiation, 2–7 h or AIBN,
strategy for the synthesis of such imidazolyl phosphanes.
65–70 °C, 6–7 h) of secondary phosphanes to 1-vinylimidazole, 2-
However, there are only two papers5 describing briefly the
methyl-1-vinylimidazole, and 1-vinylbenzimidazole proceeds regio-
addition of H-phosphanes to 1-vinylimidazoles in a
strongly basic catalytic systems. The process was per-
formed in the presence of considerable amount (more than
40 mol% in total) of KOt-Bu and n-BuLi in THF and hex-
ane as solvents.5b It took 85 hours to obtain the adduct in
69% yield.
selectively to give the corresponding anti-Markovnikov adducts in
88–98% yields.
Key words: nitrogen heterocycles, 1-vinylimidazoles, secondary
phosphanes, radical reactions, phosphane addition
In recent years, the increasing interest is focused on the
imidazolyl-substituted phosphanes as potent polydentate
ligands for the design of metal complexes.1 The latter en-
sure good performing catalysis in the hydroformylation of
To the best of our knowledge, there are no explicit exam-
ples in the literature on the free-radical addition of sec-
ondary phosphanes to 1-vinylimidazoles. Noteworthy,
such a process as atom-economic, metal-free, and waste-
less fairly meets the requirements of green chemistry.
1-octene,1b
hydration,1d
hydroamination,1j
and
hydrothiolation1j of terminal alkynes, palladium-cata-
lyzed Suzuki1e,g and Sonogashira1g coupling of aryl
halides, hydroxylation,1i and Buchwald–Hartwig
amination1e of aryl chlorides. Such hybrid ligands are
used as models to study the effects of phosphane and het-
erocyclic substituents on the coordination geometry of
metal complexes and binding affinity of the soft P and
hard N donors for specific metal.1f–h
Herein we report a simple general and atom-economic
synthesis of tertiary phosphanes bearing imidazolyl sub-
stituents by free radical addition of secondary phosphanes
to available 1-vinylimidazoles. Readily accessible sec-
ondary phosphanes used in the work were mostly those,
which are easily produced from red phosphorus and sty-
renes in one-pot procedure.6
The reaction proceeds under UV irradiation or in the pres-
ence of azaisobutyronitrile (AIBN) in dioxane at 65–
70 °C to give the anti-Markovnikov adducts in near to
quantitative yields (Table 1).7
Phosphorus-substituted imidazoles are prospective pre-
cursors in the synthesis of biologically active compounds,
since the imidazole ring is a privileged structure of a wide
range of natural products, including purines,2 imidazole-
based alkaloids, amino and nucleic acids, biotin, and vita-
min B12.3
Interestingly, secondary phosphine oxides do not add to
vinylimidazoles under the above conditions (both under
UV irradiation and in the presence of AIBN). This fact
correlates well with the known data on the low reactivity
of secondary phosphane oxides toward free radical
initiation8 due to a high P–H bond dissociation energy in
the phosphoryl moiety.9 Nevertheless, the strategy here
elaborated opens an easy access to tertiary phosphine ox-
ides 8a–g via mild quantitative oxidation of the phos-
phanes 7a–g (r.t., 12–24 h, acetone; Scheme 1).10
Meanwhile, the known syntheses of imidazolyl phos-
phanes are multistep, laborious, and based commonly on
the reactions of hazardous phosphorus halides with 2-
lithiated imidazoles.1 A less general approach to [2-(1-
alkylimidazolyl)]phosphanes is a direct C-2 phosphana-
tion of 1-alkylimidazoles by phosphane halides in pyri-
dine/triethylamine.4 This approach employing PCl3 and 1-
vinylimidazole allows tris[2-(1-vinylimidazolyl)]phos-
phane to be obtained in 29% yield only.4c
Actually, on demand, one can synthesize either tertiary
phosphanes or corresponding phosphane oxides bearing
imidazol substituents.
Therefore, the search for more straightforward and atom-
economic (‘green’) route to tertiary phosphanes bearing
imidazole and benzimidazole moieties remains a synthet-
ic challenge. The addition of secondary phosphanes to 1-
O2
r.t.
O
7a–g
N
P
N
R1
R2
SYNLETT 2011, No. 1, pp 0094–0098
x
x.
x
x.
2
0
1
0
R1
8a–g
Advanced online publication: 10.12.2010
DOI: 10.1055/s-0030-1259103; Art ID: D27210ST
© Georg Thieme Verlag Stuttgart · New York
Scheme 1 Oxidation of phosphanes 7a–g

LETTER
Hydrophosphanation of 1-Vinylimidazoles with Secondary Phosphanes
95
Table 1 Free-Radical Addition of Phosphanes 1–3 to 1-Vinylimidazoles 4–6a
N
R1
R1
UV or AIBN
dioxane
+
P
H
N
R2
R1
R1
N
N
P
R2
1–3
4–6
7a–g
Phosphane
Imidazole
Product
Conditions
Yield (%)b
N
N
UV, 3 h
AIBN, 6 h
96
98
P
PH
PH
N
N
N
4
5
7a
7b
1
1
N
N
P
UV, 3 h
96
N
N
N
UV, 7 h
AIBN, 7 h
90
88
PH
P
N
N
6
4
1
7c
t-Bu
t-Bu
N
N
P
N
PH
N
UV, 5 h
92
98
t-Bu
t-Bu
7d
2
t-Bu
t-Bu
N
N
N
P
PH
UV, 3 h
N
t-Bu
5
t-Bu
2
7e
t-Bu
t-Bu
N
N
N
PH
P
UV, 5 h
90
95
N
t-Bu
6
4
t-Bu
2
7f
N
N
N
N
UV, 2 h
P
PH
3
7g
a The ratio of phosphane/imidazole was 1:1. All experiments were carried out under argon atmosphere.
b Isolated and pure compound.
Synlett 2011, No. 1, 94–98 © Thieme Stuttgart · New York

96
B. A. Trofimov et al.
LETTER
(7) General Procedure for the Synthesis of Phosphanes 7a–g
A solution of phosphane 1–3 (1 mmol) and imidazole 4–6 (1
mmol) in dioxane (0.5 mL) was irradiated (200 W Hg arc
lamp) in a quartz ampoule (method A) or heated at 65–70
°C in the presence of AIBN (1 wt% of the total mass of
reactants) in a sealed ampoule (method B; reaction times are
given in Table 1). The reaction was monitored by 31P NMR
by disappearance of the signal of the starting phosphanes
(d = –69 to –70 ppm) and appearance of a new signal in the
region of d = –29 to –31 ppm, corresponding to tertiary
phosphanes 7a–g. Dioxane was then removed under reduced
pressure and the residue was dissolved in hexane (3 mL).
The solution was passed through a thin layer of Al2O3, and
the solvent was evaporated in vacuo to give tertiary
phosphanes 7a–g of analytical purity. All manipulations
were carried out under argon atmosphere.
In summary, a facile free-radical addition of secondary
phosphanes to 1-vinylimidazoles has been accomplished.
This simple, straightforward, and atom-economic method
represents an advantageous alternative to the known mul-
tistep and laborious syntheses of tertiary phosphanes with
imidazolyl substituents. Thus, the reaction developed
paves a short and expedient way to a family of phosphanes
bearing imidazolyl moieties, potent P,N donor ligands for
the design of metal complex catalysts, and building blocks
for organic synthesis. The results obtained contribute both
to fundamental and synthetic chemistry of phosphorus
and 1-vinylimidazoles.
Acknowledgment
Bis(2-phenethyl)-[2-(1H-imidazolyl)ethyl]phosphane
(7a)
This work has been carried out with financial support of leading sci-
entific schools by the President of the Russian Federation (Grant
NSH-263.2008.3) and the Russian Foundation of Basic Research
(Grant No. 08-03-00251).
Anal. Calcd C21H25N2P: C, 74.98; H, 7.49; N, 8.33; P, 9.21.
Found: C, 74.70; H, 7.42; N, 8.13; P, 9.08. 1H NMR (400.13
MHz, CDCl3): d = 1.63–1.83 (m, 6 H, CH2P), 2.68–2.75 (m,
4 H, CH2Ph), 3.92–3.98 (m, 2 H, CH2N), 6.84 and 7.03 (s, 2
H, H4,5 in imidazole), 7.14–7.29 (m, 10 H, Ph), 7.41 (s, 1 H,
H2 in imidazole) ppm. 13C NMR (100.62 MHz, CDCl3):
d = 29.0 (d, 2JPC = 13.7 Hz, CH2Ph), 29.43 (d, 1JPC = 16.9
Hz, PCH2CH2N), 32.28 (d, 1JPC = 15.0 Hz, CH2P), 44.70 (d,
2JPC = 22.8 Hz, CH2N), 118.54 (C4 in imidazole), 126.27 (p-
C in Ph), 128.16 (o-C in Ph), 128.62 (m-C in Ph), 129.67 (C5
in imidazole), 136.73 (C2 in imidazole), 142.19 (d, 3JPC = 9.6
Hz, ipso-C in Ph) ppm. 31P NMR (161.98 MHz, CDCl3):
d = –28.31 ppm.
References and Notes
(1) (a) Kläui, W.; Piefer, C.; Rheinwald, G.; Lang, H. Eur. J.
Inorg. Chem. 2000, 1549. (b) Brauer, D. J.; Kottsieper, K.
W.; Liek, C.; Stelzer, O.; Waffenschmidt, H.; Wasserscheid,
P. J. Organomet. Chem. 2001, 630, 177. (c) Jalil, M. A.;
Yamada, T.; Fujinami, S.; Hojo, T.; Nishikawa, H.
Polyhedron 2001, 20, 627. (d) Grotjahn, D. B.; Incarvito, C.
D.; Rheingold, A. L. Angew. Chem. Int. Ed. 2001, 40, 3884.
(e) Harkal, S.; Rataboul, F.; Zapf, A.; Fuhrmann, C.;
Riermeier, T.; Monsees, A.; Beller, M. Adv. Synth. Catal.
2004, 346, 1742. (f) Grotjahn, D. B.; Gong, Y.; Zakharov,
L.; Golen, J. A.; Rheingold, A. L. J. Am. Chem. Soc. 2006,
128, 438. (g) Debono, N.; Canac, Y.; Duhayon, C.; Chauvin,
R. Eur. J. Inorg. Chem. 2008, 2991. (h) Canac, Y.; Debono,
N.; Vendier, L.; Chauvin, R. Inorg. Chem. 2009, 48, 5562.
(i) Schulz, T.; Torborg, C.; Schäffner, B.; Huang, J.; Zapf,
A.; Kadyrov, R.; Börner, A.; Beller, M. Angew. Chem. 2009,
121, 936. (j) Field, L. D.; Messerle, B. A.; Vuong, K. Q.;
Turner, P. Dalton Trans. 2009, 3599.
Bis(2-phenethyl)[2-(2-methyl-1H-imidazolyl)ethyl]-
phosphane (7b)
Anal. Calcd C22H27N2P: C, 75.40; H, 7.77; N, 7.99; P, 8.84.
Found: C, 75.65; H, 7.74; N, 7.93; P, 8.81. 1H NMR (400.13
MHz, CDCl3): d = 1.68–1.74 (m, 6 H, PCH2), 2.32 (s, 3 H,
Me), 2.69–2.71 (m, 4 H, CH2Ph), 3.80–3.88 (m, 2 H, CH2N),
6.74 and 6.85 (s, 2 H, H4,5 in imidazole), 7.13–7.21 (m, 10 H,
Ph) ppm. 13C NMR (100.62 MHz, CDCl3): d = 12.85 (Me),
28.75 (d, 2JPC = 14.1 Hz, CH2Ph), 29.46 (d, 1JPC = 19.1 Hz,
PCH2CH2N), 32.02 (d, 1JPC = 14.6 Hz, PCH2), 43.52 (d,
2JPC = 21.8 Hz, CH2N), 118.57 (C4 in imidazole), 126.05
(p-C in Ph), 127.85 (o-C in Ph), 128.15 (C5 in imidazole),
128.49 (m-C in Ph), 141.94 (d, 3JPC = 10.9 Hz, ipso-C in Ph),
143.76 (C2 in imidazole) ppm. 31P NMR (161.98 MHz,
CDCl3): d = –31.15 ppm.
(2) (a) Steenken, S. Chem. Rev. 1989, 89, 503. (b) Parker,
W. B. Chem. Rev. 2009, 109, 2880.
(3) (a) Grimmett, M. R. In Comprehensive Heterocyclic
Chemistry II, Vol. 3; Katritzky, A. R.; Rees, C. W.; Scriven,
E. F. V., Eds.; Pergamon: Oxford, 1996, 77–220. (b) De
Luca, L. Curr. Med. Chem. 2006, 13, 1. (c) Jin, Z. Nat.
Prod. Rep. 2006, 23, 464. (d) Bellina, F.; Cauteruccio, S.;
Rossi, R. Tetrahedron 2007, 63, 4571.
(4) (a) Tolmachev, A. A.; Yurchenko, A. A.; Semenova, M. G.;
Feshchenko, N. G. Zh. Obshch. Khim. 1993, 63, 714; Chem.
Abstr. 1993, 119, 180912f. (b) Tolmachev, A. A.;
Yurchenko, A. A.; Merculov, A. S.; Semenova, M. G.;
Zarudnitskii, E. V.; Ivanov, V. V.; Pinchuk, A. M. Heteroat.
Chem. 1999, 10, 585. (c) Schiller, A.; Scopelliti, R.;
Benmelouka, M.; Severin, K. Inorg. Chem. 2005, 44, 6482.
(5) (a) Kottsieper, K. W.; Stelzer, O.; Wasserscheid, P. J. Mol.
Catal. A: Chem. 2001, 175, 285. (b) Miranda-Soto, V.;
Grotjahn, D. B.; DiPasquale, A. G.; Rheingold, A. L. J. Am.
Chem. Soc. 2008, 130, 13200.
(6) (a) Trofimov, B. A.; Brandsma, L.; Arbuzova, S. N.;
Malysheva, S. F.; Gusarova, N. K. Tetrahedron Lett. 1994,
35, 7647. (b) Gusarova, N. K.; Malysheva, S. F.; Kuimov,
V. A.; Belogorlova, N. A.; Mikhailenko, V. L.; Trofimov, B.
A. Mendeleev Commun. 2008, 18, 260. (c) Trofimov, B. A.;
Gusarova, N. K. Mendeleev Commun. 2009, 19, 295.
Bis(2-phenethyl)[2-(1H-1,3-benzimidazolyl)ethyl]-
phosphane (7c)
Anal. Calcd C25H27N2P: C, 77.70; H, 7.04; N, 7.25; P, 8.01.
Found: C, 77.68; H, 7.06; N, 7.21; P, 8.30. 1H NMR (400.13
MHz, CDCl3): d = 1.65–1.71 (m, 4 H, PCH2), 1.86–1.89 (m,
2 H, PCH2CH2N), 2.65–2.66 (m, 4 H, CH2Ph), 4.12–4.17
(m, 2 H, CH2N), 7.08–7.29 (m, 12 H, Ph, H5,6 in imidazole),
7.32, 7.81 and 7.83 (m, 3 H, H4,7,2 in imidazole) ppm.
13C NMR (100.62 MHz, CDCl3): d = 27.70 (d, 1JPC = 17.1
Hz, PCH2CH2N,), 28.76 (d, 2JPC = 13.9 Hz, CH2Ph), 32.0 (d,
1JPC = 14.3 Hz, PH2), 42.64 (d, 2JPC = 23.4 Hz, CH2N),
109.40 (C7 in imidazole), 120.36 (C4 in imidazole), 122.02
(C6 in imidazole), 122.76 (C5 in imidazole), 126.06 (p-C in
Ph), 127.97 (o-C in Ph), 128.60 (m-C in Ph), 133.24 (C8 in
imidazole), 141.96 (d, 3JPC = 10.9 Hz, ipso-C in Ph), 142.42
(C2 in imidazole), 143.81 (C9 in imidazole) ppm. 31P NMR
(161.98 MHz, CDCl3): d = –30.96 ppm.
Bis[2-(4-tert-butylphen)ethyl][2-(1H-imidazolyl)ethyl]-
phosphane (7d)
Anal. Calcd C29H41N2P: C, 77.64; H, 9.21; N, 6.24; P, 6.90.
Found: C, 77.66; H, 9.20; N, 6.21; P, 6.76. 1H NMR (400.13
Synlett 2011, No. 1, 94–98 © Thieme Stuttgart · New York

LETTER
Hydrophosphanation of 1-Vinylimidazoles with Secondary Phosphanes
97
MHz, CDCl3): d = 1.27 (s, 18 H, Me), 1.66–1.77 (m, 6 H,
(9) Jessop, C. M.; Parsons, A. F.; Routledge, A.; Irvine, D. J.
Eur. J. Org. Chem. 2006, 1547.
(10) General Procedure for the Preparation of the Phosphane
Oxides 8a–g
PCH2), 2.66–2.68 (m, 4 H, CH2C6H4), 3.94–3.97 (m, 2 H,
CH2N), 6.83 and 7.02 (s, 2 H, H4,5 in imidazole), 7.08–7.10
and 7.29–7.31 (m, 8 H, C6H4), 7.43 (s, 1 H, H2 in imidazole)
ppm. 13C NMR (100.62 MHz, CDCl3): d = 28.90 (d,
2JPC = 12.7 Hz, CH2C6H4), 29.43 (d, 1JPC = 19.4 Hz,
PCH2CH2N), 31.47 (Me), 31.76 (d, 1JPC = 19.6 Hz, CH2P),
34.50 (C-Me), 44.82 (d, 2JPC = 20.3 Hz, CH2N), 118.62 (C4
in imidazole), 125.59 (o-C in C6H4), 125.84 (C5 in
imidazole), 127.87 (m-C in C6H4), 136.69 (C2 in imidazole),
139.18 (d, 3JPC = 10.9 Hz, ipso-C in C6H4), 149.15 (p-C in
C6H4) ppm. 31P NMR (161.98 MHz, CDCl3): d = –29.80
ppm.
A solution of phosphane 7a–g (1 mmol) in acetone was
stirred at r.t. under air atmosphere. After reaction
completion, as indicated by TLC, the solvent was removed
under reduced pressure to afford phosphane oxide 8a–g.
Bis(2-phenethyl)[2-(1H-imidazolyl)ethyl]phosphane
Oxide (8a)
Yield 349 mg (99%), colorless crystalline solid, mp 99–
102 °C (hexane). Anal. Calcd C21H25N2OP: C, 71.57; H,
7.15; N, 7.95; P, 8.79. Found: C, 71.47; H, 7.12; N, 7.83; P,
8.71. 1H NMR (400.13 MHz, CDCl3): d = 1.91–2.08 (m, 6
H, CH2P), 2.83–2.87 (m, 4 H, CH2Ph), 4.16–4.23 (m, 2 H,
CH2N), 6.86 and 7.03 (s, 2 H, H4,5 in imidazole), 7.16–7.28
(m, 10 H, Ph), 7.48 (s, 1 H, H2 in imidazole) ppm. 13C NMR
(100.62 MHz, CDCl3): d = 27.55 (d, 2JPC = 3.2 Hz, H2Ph),
30.36 (d, 1JPC = 60.1 Hz, PCH2CH2N), 30.56 (d, 1JPC = 63.2
Hz, CH2P), 40.14 (CH2N), 118.64 (C4 in imidazole), 126.68
(p-C in Ph), 128.0 (o-C in Ph), 128.75 (m-C in Ph), 129.60
(C5 in imidazole), 136.91 (C2 in imidazole), 140.13 (d,
3JPC = 11.0 Hz, ipso-C in Ph) ppm. 31P NMR (161.98 MHz,
CDCl3): d = 43.56 ppm.
Bis[2-(4-tert-butylphen)ethyl][2-(2-methyl-1H-
imidazolyl)ethyl]phosphane (7e)
Anal. Calcd C30H43N2P: C, 77.88; H, 9.37; N, 6.06; P, 6.69.
Found: C, 77.67; H, 9.34; N, 6.10; P, 6.63. 1H NMR (400.13
MHz, CDCl3): d = 1.28 (s, 18 H, MeC6H4), 1.67–1.75 (m, 6
H, PCH2), 2.30 (s, 3 H, Me), 2.68–2.70 (m, 4 H, CH2C6H4),
3.80–3.85 (m, 2 H, CH2N), 6.75 and 6.80 (s, 2 H, H4,5 in
imidazole), 7.13–7.23 (m, 8 H, C6H4) ppm. 13C NMR
(100.62 MHz, CDCl3): d = 13.01 (Me), 28.76 (d, 2JPC = 14.3
Hz, CH2C6H4), 29.49 (d, 1JPC = 18.8 Hz, PCH2CH2N), 31.47
(MeC6H4), 32.46 (d, 1JPC = 14.6 Hz, CH2P), 34.50 (C-Me),
43.82 (d, 2JPC = 22.3 Hz, CH2N), 118.52 (C4 in imidazole),
126.09 (o-C in C6H4), 127.53 (C5 in imidazole), 127.77
(m-C in C6H4), 141.95 (d, 3JPC = 10.7 Hz, ipso-C in C6H4),
143.76 (C2 in imidazole), 144.15 (p-C in C6H4) ppm.
31P NMR (161.98 MHz, CDCl3): d = –31.20 ppm.
Bis[2-(4-tert-butylphen)ethyl][2-(1H-1,3-
Bis(2-phenethyl)[2-(2-methyl-1H-imidazolyl)ethyl]-
phosphane Oxide (8b)
Yield 359 mg (98%), light-yellow oil. Anal. Calcd
C22H27N2OP: C, 72.11; H, 7.43; N, 7.64; P, 8.45. Found: C,
72.15; H, 7.44; N, 7.63; P, 8.41. 1H NMR (400.13 MHz,
CDCl3): d = 1.94–2.01 (m, 6 H, PCH2), 2.36 (s, 3 H, Me),
2.83–2.87 (m, 4 H, CH2Ph), 4.08–4.14 (m, 2 H, CH2N), 6.78
and 6.87 (s, 2 H, H4,5 in imidazole), 7.13–7.21 (m, 10 H, Ph)
ppm. 13C NMR (100.62 MHz, CDCl3): d = 12.85 (Me),
27.51 (CH2Ph), 29.62 (d, 1JPC = 60.2 Hz, PCH2CH2N), 30.49
(d, 1JPC = 63.5 Hz, CH2P), 38.99 (CH2N), 118.71 (C4 in
imidazole), 126.52 (p-C in Ph), 127.93 (o-C in Ph), 128.55
(C5 in imidazole), 128.83 (m-C in Ph), 140.07 (d, 3JPC = 11.8
Hz, ipso-C in Ph), 144.12 (C2 in imidazole) ppm. 31P NMR
(161.98 MHz, CDCl3): d = 45.31 ppm.
benzimidazolyl)ethyl]phosphane (7f)
Anal. Calcd C33H43N2P: C, 79.48; H, 8.69; N, 5.62; P, 6.21.
Found: C, 79.40; H, 8.61; N, 5.58; P, 6.11. 1H NMR (400.13
MHz, CDCl3): d = 1.28 (s, 18 H, Me), 1.68–1.75 (m, 4 H,
CH2P), 1.93–1.98 (m, 2 H, PCH2CH2N), 2.64–2.71 (m, 4 H,
CH2C6H4), 4.19–4.25 (m, 2 H, CH2N), 6.81 and 6.98 (m, 2
H, H5,6 in imidazole), 7.03–7.07 and 7.28–7.31 (m, 9 H,
C6H4, H4 in imidazole), 7.79 and 7.85 (s, 2 H, H7,2 in
imidazole) ppm. 13C NMR (100.62 MHz, CDCl3): d = 27.76
(d, 1JPC = 17.1 Hz, CH2CH2N), 28.70 (d, 2JPC = 13.9 Hz,
CH2C6H4), 31.27 (Me), 31.48 (d, 1JPC = 15.5 Hz, CH2P),
34.26 (CMe), 42.72 (d, 2JPC = 23.1 Hz, CH2N), 109.41
(C7 in imidazole), 120.40 (C4 in imidazole), 122.10 (C6 in
imidazole), 122.86 (C5 in imidazole), 125.28 (o-C in C6H4),
127.72 (m-C in C6H4), 133.26 (C8 in imidazole), 138.95 (d,
3JPC = 10.9 Hz, ipso-C in C6H4), 142.41 (C2 in imidazole),
143.73 (C9 in imidazole), 148.97 (p-C in C6H4) ppm.
31P NMR (161.98 MHz, CDCl3): d = –31.15 ppm.
Bis(phenhyl)-[2-(1H-imidazolyl)ethyl]phosphane (7g)
Anal. Calcd C17H17N2P: C, 72.84; H, 6.11; N, 9.99; P, 11.05.
Found: C, 72.80; H, 6.12; N, 9.93; P, 11.01. 1H NMR
(400.13 MHz, CDCl3): d = 2.48–2.52 (m, 2 H, CH2P), 3.96–
4.01 (m, 2 H, CH2N), 6.85 and 7.01 (m, 2 H, H4,5 in
imidazole), 7.31–7.71 (m, 10 H, Ph), 8.67 (s, 1 H, H2 in
imidazole) ppm. 13C NMR (100.62 MHz, CDCl3): d = 30.51
(d, 1JPC = 14.8 Hz, CH2P), 44.13 (d, 2JPC = 23.5 Hz, CH2N),
118.54 (C4 in imidazole), 128.89 (d, 3JPC = 13.4 Hz, m-C in
Ph), 129.16 (p-C in Ph), 129.57 (C5 in imidazole), 130.69 (d,
2JPC = 11.4 Hz, o-C in Ph), 132.61 (d, 1JPC = 19.1 Hz, ipso-C
in Ph), 136.77 (C2 in imidazole) ppm. 31P NMR (161.98
MHz, CDCl3): d = –20.84 ppm.
Bis(2-phenethyl)[2-(1H-1,3-benzimidazolyl)ethyl]-
phosphane Oxide (8c)
Yield 398 mg (99%), colorless crystalline solid, mp 190–
200 °C (hexane). Anal. Calcd C25H27N2OP: C, 74.61; H,
6.76; N, 6.96; P, 7.70. Found: C, 74.67; H, 6.56; N, 6.87; P,
7.75. 1H NMR (400.13 MHz, CDCl3): d = 1.85–1.92 (m, 4
H, PCH2), 2.11–2.17 (m, 2 H, PCH2CH2N), 2.74–2.79 (m, 4
H, CH2Ph), 4.41–4.48 (m, 2 H, CH2N), 7.03–7.27 (m, 12 H,
Ph, H5,6 in imidazole), 7.35 (s, 1 H, H4 in imidazole), 7.76
and 7.92 (m, 2 H, H7,2 in imidazole) ppm. 13C NMR (100.62
MHz, CDCl3): d = 27.55 (CH2Ph), 28.36 (d, 2JPC = 60.0 Hz,
PCH2CH2N), 30.67 (d, 1JPC = 62.0 Hz, CH2P), 38.26
(CH2N), 109.41 (C7 in imidazole), 120.52 (C4 in imidazole),
122.48 (C6 in imidazole), 123.27 (C5 in imidazole), 126.64
(p-C in Ph), 127.96 (o-C in Ph), 128.72 (m-C in Ph), 132.99
(C8 in imidazole), 140.04 (d, 3JPC = 12.5 Hz, ipso-C in Ph),
142.93 and 143.65 (C2,9 in imidazole) ppm. 31P NMR
(161.98 MHz, CDCl3): d = 43.95 ppm.
Bis[2-(4-tert-butylphen)ethyl][2-(1H-imidazolyl)ethyl]-
phosphane Oxide (8d)
Yield 455 mg (98%), colorless crystalline solid, mp 140–
141 °C (hexane). Anal. Calcd C29H41N2OP: C, 74.97; H,
8.89; N, 6.03; P, 6.67. Found: C, 74.86; H, 8.95; N, 6.21; P,
6.76. 1H NMR (400.13 MHz, CDCl3): d = 1.29 (s, 18 H,
Me), 1.95–2.06 (m, 6 H, PCH2), 2.71–2.83 (m, 4 H, CH2Ph),
4.20–4.22 (m, 2 H, CH2N), 6.84 (s, 1 H, H4 in imidazole),
7.04–7.32 (m, 9 H, C6H4, H5 in imidazole), 7.46 (s, H2 in
imidazole) ppm. 13C NMR (100.62 MHz, CDCl3): d = 27.11
(8) (a) Leca, D.; Fensterbank, L.; Lacôte, E.; Malakria, M.
Chem. Soc. Rev. 2005, 34, 858. (b) Coudray, L.;
Montchamp, J.-L. Eur. J. Org. Chem. 2008, 3601.
(c) Trofimov, B. A.; Gusarova, N. K.; Chernysheva, N. A.;
Yas’ko, S. V.; Kazantseva, T. I.; Ushakov, I. A. Synthesis
2008, 2743.
Synlett 2011, No. 1, 94–98 © Thieme Stuttgart · New York

98
B. A. Trofimov et al.
LETTER
(CH2Ph), 30.47 (d, 1JPC = 60.7 Hz, PCH2CH2N), 30.54 (d,
1JPC = 62.7 Hz, CH2P), 31.29 (Me), 34.40 (CMe), 40.26
(CH2N), 118.69 (C4 in imidazole), 125.67 (o-C in C6H4),
127.73 (m-C in C6H4), 129.66 (C5 in imidazole), 136.93 (d,
3JPC = 12.6 Hz, ipso-C in Ph), 149.23 and 149.82 (C2 in
imidazole and p-C in C6H4) ppm. 31P NMR (161.98 MHz,
CDCl3): d = 44.86 ppm.
CDCl3): d = 1.25 (s, 18 H, Me), 1.88–2.03 (m, 4 H, CH2P),
2.14–2.18 (m, 2 H, PCH2CH2N), 2.76–2.78 (m, 4 H,
CH2Ph), 4.45–4.51 (m, 2 H, CH2N), 6.98 and 7.01 (s, 2 H,
H5,6 in imidazole), 7.24–7.34 (m, 8 H, C6H4), 7.39 (s, 1 H, H4
in imidazole), 7.78 (s, 1 H, H7 in imidazole), 7.91 (s, 1 H, H2
in imidazole) ppm. 13C NMR (100.62 MHz, CDCl3):
d = 27.13 (CH2Ph), 28.54 (d, 1JPC = 60.0 Hz, PCH2CH2N),
30.65 (d, 1JPC = 62.6 Hz, CH2P), 31.26 (Me), 34.33 (CMe),
38.30 (CH2N), 109.35 (C7 in imidazole), 120.60 (C4 in
imidazole), 122.49 (C6 in imidazole), 123.29 (C5 in
imidazole), 125.61 (o-C in C6H4), 127.63 (m-C in C6H4),
134.91 (C8 in imidazole), 136.94 (d, 3JPC = 11.4 Hz, ipso-C
in C6H4), 142.83 (C2 in imidazole), 143.72 (C9 in imidazole),
149.61 (p-C in C6H4) ppm. 31P NMR (161.98 MHz, CDCl3):
d = 44.83 ppm.
Bis[2-(4-tert-butylphen)ethyl][2-(2-methyl-1H-
imidazolyl)ethyl]phosphane Oxide (8e)
Yield 464 mg (97%), colorless crystalline solid, mp 134–
136 °C (hexane). Anal. Calcd C30H43N2OP: C, 75.28; H,
8.05; N, 5.85; P, 6.47. Found: C, 75.36; H, 8.25; N, 6.01; P,
6.56. 1H NMR (400.13 MHz, CDCl3): d = 1.28 (s, 18 H,
Me), 1.94–2.05 (m, 6 H, CH2P), 2.41 (s, 3 H, Me in
imidazole), 2.82–2.84 (m, 4 H, CH2C6H4), 4.11–4.18 (m, 2
H, CH2N), 6.76 and 6.91 (s, 2 H, H4,5 in imidazole), 7.07–
7.10 and 7.25–7.32 (m, 8 H, C6H4) ppm. 13C NMR (100.62
MHz, CDCl3): d = 12.95 (Me in imidazole), 27.25 (d,
2JPC = 3.0 Hz, CH2C6H4), 29.82 (d, 1JPC = 61.9 Hz,
PCH2CH2N), 30.62 (d, 1JPC = 64.1 Hz, CH2P), 31.44 (Me),
34.53 (CMe), 39.45 (CH2N), 118.89 (C4 in imidazole),
125.85 (o-C in C6H4), 127.22 (C5 in imidazole), 127.80 (m-
C in C6H4), 137.13 (d, 3JPC = 12.8 Hz, ipso-C in C6H4),
Bis(phenyl)-[2-(1H-imidazolyl)ethyl]phosphane Oxide
(8g)
Yield 287 mg (97%), colorless crystalline solid, mp 38–
39 °C (hexane). Anal. Calcd C17H17N2OP: C, 68.91; H, 5.78;
N, 9.45; P, 10.45. Found: C, 68.89; H, 5.77; N, 9.43; P,
10.41. 1H NMR (400.13 MHz, CDCl3): d = 2.77–2.78 (m, 2
H, CH2P), 4.28–4.30 (m, 2 H, CH2N), 6.88 and 6.93 (s, 2 H,
H4,5 in imidazole), 7.27–7.70 (m, 10 H, Ph), 8.04 (s, 1 H, H2
in imidazole) ppm. 13C NMR (100.62 MHz, CDCl3):
d = 32.15 (d, 1JPC = 67.7 Hz, CH2P), 40.43 (CH2N), 118.69
(C4 in imidazole), 128.91 (d, 3JPC = 12.3 Hz, m-C in Ph),
129.96 (C5 in imidazole), 130.47 (d, 2JPC = 9.5 Hz, o-C in
Ph), 131.56 (d, 1JPC = 100.3 Hz, ipso-C in Ph), 136.77 (C2 in
imidazole) ppm. 31P NMR (161.98 MHz, CDCl3): d = 29.46
ppm.
144,38 (C2 in imidazole), 149.80 (p-C in C6H4) ppm. 31
NMR (161.98 MHz, CDCl3): d = 44.74 ppm.
P
Bis[2-(4-tert-butylphen)ethyl][2-(1H-1,3-benzimidazolyl)-
ethyl]phosphane Oxide (8f)
Yield 509 mg (99%); light-yellow oil. Anal. Calcd
C33H43N2OP: C, 77.01; H, 8.42; N, 5.44; P, 6.02. Found: C,
77.17; H, 8.50; N, 5.73; P, 6.11. 1H NMR (400.13 MHz,
Synlett 2011, No. 1, 94–98 © Thieme Stuttgart · New York

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