Simple and efficient preparation of sterically protected 1,4-diphosphafulvenes

Article abstract of DOI:10.1016/j.tet.2005.03.080

A new synthetic method for sterically protected 1,4-diphosphafulvenes (2-methylene-2,3-dihydro-1H-[1,3]diphospholes) has been developed starting from (arylethynyl)phosphines and ca. 0.25 molar amount of butyllithium. The catalytic mechanism of the reaction is discussed based on the results of deuterium-labelling experiments.

Full text of DOI:10.1016/j.tet.2005.03.080

Tetrahedron 61 (2005) 5223–5228
Simple and efficient preparation of sterically protected
1,4-diphosphafulvenes
*
Akitake Nakamura, Kozo Toyota and Masaaki Yoshifuji
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba, Sendai 980-8578, Japan
Received 2 February 2005; revised 22 March 2005; accepted 23 March 2005
Available online 14 April 2005
Abstract—A new synthetic method for sterically protected 1,4-diphosphafulvenes (2-methylene-2,3-dihydro-1H-[1,3]diphospholes) has
been developed starting from (arylethynyl)phosphines and ca. 0.25 molar amount of butyllithium. The catalytic mechanism of the reaction is
discussed based on the results of deuterium-labelling experiments.
q 2005 Elsevier Ltd. All rights reserved.
1. Introduction
Heterocycles containing heavier main group elements have
long been compounds of importance in many research fields
such as medicinal chemistry and materials chemistry. For
example, fulvenes and fulvalenes containing hetero atoms
have been of interest. Since the discovery of the first
organic metal, tetrathiafulvalene-tetracyanoquinodimethane
(TTF-TCNQ), the quest for new synthetic metals and
superconductors has been very active.1 Thus, 2-methylene-
2,3-dihydro-1H-[1,3]dichalcogenole derivatives have
attracted much attention, because of their high p electron-
donating properties.2 In contrast, research on 2-methylene-
2,3-dihydro-1H-[1,3]diphosphole has been limited until
now.
Very recently, we have reported the formation of 2,6-
diphenyl-1,4-bis(2,4,6-tri-t-butylphenyl)-1,4-diphospha-
1,4-dihydrofulvene (or 2-benzylidene-4-phenyl-2,3-
bis(2,4,6-tri-t-butylphenyl)-2,3-dihydro-1H-[1,3]diphos-
phole) (Chart 1, 1a)3 in 37% yield together with 3-phenyl-1-
(2,4,6-tri-t-butylphenyl)-1-phosphaallene (2a,4 5%) and a
Chart 1.
trace amount of 3,4-diphosphinidenecyclobutene derivative
3a (hereafter, 3,4-diphosphinidenecyclobutene, abbreviated
as DPCB),5 when (Z)-2-bromo-2-benzyl-1-(2,4,6-tri-t-
butylphenyl)phosphaethene (4) was allowed to react with
phosphorus version of the Arduengo carbene7 and ketones
or aldehydes. In the course of our continuing investigation
of preparations and properties of DPCB derivatives,8 we
found that ethynylphosphines 6 (starting compounds in the
syntheses of DPCB derivatives, Scheme 1) also afford 1
2 molar amount of potassium t-butoxide. X-ray analysis of
(E)-1a as well as a CV study was also reported.3
Alternatively, Le Floch et al. reported the synthesis of a
series of 1,4-diphosphafulvene derivative,6 such as 5, from a
under certain conditions. Here, we report a simple and
Keywords: Phosphorus heterocycles; Phosphines; Phosphaallenes; Steric
convenient method for the preparation of 1,4-diphosphaful-
and strain effects.
venes starting from ethynylphosphines bearing a bulky
2,4,6-tri-t-butylphenyl substituent9 (abbreviated as Mes*).10
*
Corresponding author. Tel.: C81 22 795 6558; fax: C81 22 795 6562;
e-mail: yoshifj@mail.tains.tohoku.ac.jp
0040–4020/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2005.03.080

5224
A. Nakamura et al. / Tetrahedron 61 (2005) 5223–5228
2. Results and discussion
2.1. Preparation of 1,4-diphosphafulvenes
It has been established that a successive reaction of
sterically protected ethynylphosphine 6 with n- or t-BuLi
(1 molar amount) and 1,2-dibromoethane (0.5 molar
amount) affords DPCB derivative 3,8a–f as exemplified by
the preparation of 3e: Reaction of [(3-pyridyl)ethynyl]-
phosphine 6e with n-BuLi (1 molar amount) followed by
reaction with 1,2-dibromoethane (0.5 molar amount) in
THF at K78 8C affords the corresponding DPCB derivative
3e in 21% yield based on the starting (2,4,6-tri-t-
butylphenyl)-phosphine11 (Scheme 1). In this reaction, it
is likely that lithium [(3-pyridyl)ethynyl]phosphide reacts
with 1,2-dibromoethane (0.5 molar amount) to form 0.5
molar amount of (bromo)[(3-pyridyl)ethynyl]phosphine.
Coupling between the lithium phosphide and the (bromo)
(pyridylethynyl)phosphine, followed by Cope rearrange-
ment and electrocyclization, affords 3e.
Scheme 2.
interesting discovery: Reactions of 6a–e with n-BuLi (ca.
0.25 molar amount) in the absence of 1,2-dibromoethane at
room temperature afforded 1a–e (for purification of 1a–e,
see below), probably via a reaction between in situ prepared
1-phosphaallene 2a–e and phosphaallenyl anion 8a–e as
shown in Schemes 2 and 3. This route includes three
important steps A, B, and C. Step A (Scheme 2) is a very fast
catalytic cycle, which involves, (i) partial lithiation of
ethynylphosphine 6 with n-BuLi to form phosphide 7,
(ii) rearrangement of the anion 7 to the anion 8,13 and
(iii) protonation of 8 by the starting ethynylphosphine 6 to
form 2 and regenerate 8 (via 7). Step B (Scheme 3) is a
reaction between 2 (formed at Step A) and 8 to form 9. Step
B seems to proceed in a stepwise manner rather than a
concerted manner, as shown in Scheme 4: compounds 2 and
8 first, react in a sterically less hindered manner, then bond
rotation around the phosphorus-vinyl bond occurs, followed
by cyclization in a sterically more congested manner to give
Scheme 1.
However, when a 2-pyridyl isomer 6f (Scheme 2) was
allowed to react with n-BuLi and 1,2-dibromoethane under
similar conditions (crude 6f was used because separation of
6f from other products proved difficult), we found that 1f
instead of 3f was formed by 31P NMR spectroscopic
monitoring, although only in trace yield due to difficulties in
separation and purification [1.2% yield from starting
Mes*PH2, 1f: Orange solid, mp 237–239 8C (decomp.);
2
31P{1H} NMR (162 MHz, CDCl3) dZ28.0 (d, JPPZ
2
26.2 Hz) and 47.1 (d, JPPZ26.2 Hz). HRMS (SIMS).
Found m/z 759.4934. Calcd for C50H68N2P2: MCCH,
759.4930]. This striking contrast prompted us to investigate
reaction conditions of 6a–e12 with n-BuLi which led to an
Scheme 3.

A. Nakamura et al. / Tetrahedron 61 (2005) 5223–5228
5225
THF at room temperature yielded 1a as a mixture of E- and
Z-isomers [(E)-1a:(Z)-1aZ2.7:1, determined by 31P NMR
spectroscopy]. We obtained (E)-1a in 55% isolated yield
(Table 1, entry 2).
We then carried out a reaction of ethynylphosphine 6a using
0.25 molar amount of n-BuLi. A clean reaction proceeded to
afford 1a in 70% isolated yield (Table 1, entry 1), which
supports the above catalytic mechanism. Furthermore, we
examined the protonation step of 9 with 2, using deuterated
1-phosphaallene 2ad (Chart 2). Reaction of 2ad (97% D)
with 0.26 molar amount of t-BuLi in THF at room temper-
ature (generation of phosphaallenyllithium 8a) yielded a
dideuterated diphosphafulvene 1ad2 in 38% isolated yield
with good D-incorporation, (91% D on the exo-methylene
carbon and 73% D at the 3-position of the 1,4-dihydro-
Scheme 4.
Table 1. Preparation and oxidation potential of (E)-1a–e
Entry
Phosphine
R
n-BuLia
Product
Yieldb/%
E1/2/Vc
1
2
3
4
5
6
6a
6a
6b
6c
6d
6e
Ph
Ph
0.25d
0.50
1a
1a
1b
1c
1d
1e
70
55
46
38e
52
61
0.02
4-MeOC6H4
o-Tol
3-Thienyl
3-Pyridyl
0.25d
0.30d
0.30d
0.20d
K0.05
0.01e
0.03
0.20
a Molar amount based on 6.
b Yields were calculated taking the reaction mechanism into account (two molecules of 6 give one molecule of 1).
c Conditions: 1 mM in CH2Cl2 with 0.1 M n-Bu4NClO4 as support electrolyte. Working electrode: glassy carbon; Counter electrode: Pt wire; Reference
electrode: Ag/0.01 M AgNO3 in acetonitrile with 0.1 M n-Bu4NClO4 [E1/2 (Fc/FcC)Z0.23 V]; Scan rate: 100 mV/s.
d Optimized data. The experiments were carried out using either 0.15, 0.20, 0.25, 0.30, 0.40, or 0.50 molar amounts of n-BuLi.
e Mixture of (E)- and (Z)-isomers.
(E)-1 as a major product. The cyclization is likely a
kinetically controlled reaction, due to the difficulty of
inversion of the sp2-carbanion.
fulvene ring) which also supports the mechanism via 8a and
9ad (Steps B and C). It should be mentioned that the
expected maximum D-content at the 3-position is 74% D,
based on the above mechanism, because 0.26 molar amount
of t-BuLi were used to initiate the reaction by abstraction of
First, we thought 1 is simply a quenched product of 9, but
the mechanism turned out to be not so straightforward
according to the following experimental results. Step C
(Scheme 3) is considered to operate as the final step of this
mechanism. Intermediate 9 appears to be protonated by the
remaining 1-phosphaallene 2, before work-up (see below),
and regenerates the phosphaallenyl anion 8.
D
in the absence of butyllithium.
C from 2ad. It should also be noted that 2a did not form 1a
The scope and limitations of this methodology were then
investigated. Reactions of ethynylphosphines 6b–e afforded
(E)-1b–e and (Z)-1b–e (Table 1). Although (E)-1c and
(Z)-1c were not separated from the mixture, compounds
(E)-1b,d,e were isolated. However, when ethynyl-
phosphines 6 bearing primary alkyl (RZn-Bu), secondary
alkyl (RZcyclohexyl), tertiary alkyl (RZt-Bu), trimethyl-
silyl, (t-butyldimethylsilyloxy)methyl, or p-(trifluoromethyl)-
phenyl were employed, the results were unsatisfactory due to
partial formation of the corresponding phosphaallenes.
Attempted deuteration of intermediate 9a by addition of
methanol-d4 failed, suggesting that the protonation of 9
occurs before addition of methanol-d4. Thus, a catalytic
amount of 8 formed in situ is expected to convert two
molecules of phosphaallene 2 to 1. Indeed, the reaction of
ethynylphosphine 6a with 0.5 molar amount of n-BuLi in
It should be noted that Table 1 (entries 1, 3–6) shows
optimized result with respect to the molar amount of
butyllithium. When less butyllithium than the optimized
amount was used, recovery of the starting ethynylphosphine
6 increased. When more butyllithium than the optimized
amount was used, yield of the by-product 2 increased.
2.2. Cyclic voltammogram of 1,4-diphosphafulvenes
Results of cyclic voltammetric measurements of compounds
1b–e in dichloromethane are shown in Table 1, together
with that of 1a.3 All compounds showed reversible
Chart 2.

5226
A. Nakamura et al. / Tetrahedron 61 (2005) 5223–5228
oxidation peaks. Among the five 1,4-diphosphafulvenes, 1b
showed the lowest oxidation potential and the order was
1b ! 1c ! 1a ! 1d ! 1e. This tendency indicates that
electron-donating substituents lower the oxidation poten-
tials. The compounds 1a–e showed relatively good electron-
donating activities with Eox values ranging from K0.05 to
0.20 V. This relatively large range for the Eox values of 1
indicates significant effects of the substituent at the 2- or
6-positions on the redox properties of 1 and the tendency
found here may become a good guide for developing new
material containing the diphosphafulvene structure.
Compound (E)-1b. Yellow solid, mp 185–188 8C
1
(decomp.); H NMR (600 MHz, CDCl3) dZ1.35 (18H, s,
p-t-Bu), 1.64 (36H, br, o-t-Bu), 3.70 (3H, s, OCH3), 3.75
3
(3H, s, OCH3), 6.28 (2H, d, JHHZ8.4 Hz, o-arom.), 6.43
3
(2H, d, 3JHHZ8.4 Hz, m-arom.), 6.45 (1H, dd, JPHZ19.8,
3
6.6 Hz, CHAnis), 6.66 (2H, d, JH3HZ8.4 Hz, m-arom.0),
2
6.69 (1H, dd, JPHZ37.2 Hz and JPHZ13.2 Hz, PCH),
3
7.07 (2H, d, JHHZ8.4 Hz, o-arom.0), and 7.51 (4H, br,
m-Mes*); 13C{1H} NMR (151 MHz, CDCl3) dZ31.2 (s,
p-CMe3), 31.3 (s, p-CMe3), 33.5 (br, o-CMe3), 34.0 (br,
o-CMe3), 34.7 (s, p-CMe3), 34.9 (s, p-CMe3), 39.6 (d,
3JPCZ4.5 Hz, o-CMe3), 39.8 (br, o-CMe3), 55.0 (s, OCH3),
55.1 (s, OCH3), 113.1 (s, Anis), 113.2 (s, Anis), 123.5 (br,
m-Mes*), 124.8 (dd, 1JPCZ22.6 Hz, 2JPCZ10.6 Hz, PCH),
3. Conclusion
3
4
127.9 (dd, JPCZ4.5 Hz, JPCZ1.5 Hz, Anis), 128.9
4
1
In summary, we have developed a new synthetic method-
ology for diphosphafulvene via sterically protected
1-phosphaallene intermediates. The reaction mechanism
turned out interestingly to involve phosphaallenyllithium as
catalyst. As the experimental procedure is simple and the
starting ethynylphosphines are easily prepared from (2,4,6-
tri-t-butylphenyl)phosphine, these facts merit this
preparation method.
(dd, JPCZ5.3 Hz, 2.3 Hz, Anis), 129.2 (d, JPCZ61.9 Hz,
1 3
ipso-Mes*), 129.3 (dd, JPCZ61.9 Hz, JPCZ3.0 Hz, ipso-
Mes*), 130.9 (dd, 2JPCZ21.9 Hz, 3JPCZ2.3 Hz, ipso-Anis),
131.3 (d, JPCZ4.5 Hz, ipso-Anis), 131.4 (dd, JPC
3
1
Z
2
42.3 Hz, 34.7 Hz, PCP), 134.6 (dd, JPCZ27.2 Hz,
24.1 Hz, CHAnis), 142.1 (t, JPCZ14.3 Hz, PCAnis), 150.6
(s, p-Mes*), 150.6 (s, p-Mes*), 151.6 (s, o-Mes*), 151.6 (s,
o-Mes*), 157.5 (s, Anis), and 158.5 (s, Anis); 31P{1H} NMR
(162 MHz, CDCl3) dZ53.8 (d, 2JPPZ22.5 Hz) and 23.1 (d,
2JPPZ22.5 Hz); UV–Vis (hexane) 256 (log 3 4.54), 295 (sh,
4.45), and 406 nm (3.92); IR (KBr) n/cmK1 2958, 2906,
2833, 1601, 1504, 1466, 1392, 1360, 1294, 1248, 1211,
1176, 1117, 1038, 874, 804, and 754. HRMS (ESI). Found
m/z 816.5162. Calcd for C54H74O2PC2 : MC, 816.5159.
Found: C, 74.97; H, 8.91%. Calcd for C54H74O2P2$3H2O:
C, 74.45; H, 9.26%.
4. Experimental
4.1. General
Melting points were measured on a Yanagimoto MP-J3
micro melting point apparatus and were uncorrected. NMR
spectra were recorded on a Bruker Avance-400 or a Bruker
AM-600 spectrometer. IR spectra were obtained on a Horiba
FT-300 spectrometer. FT-ICR-MS spectra were measured
on a Bruker APEX III spectrometer. Cyclic voltammograms
were recorded on a BAS-CV-50W voltammetric analyzer
under nitrogen. Reactions were performed under an argon
atmosphere while work-up was carried out in air, unless
otherwise specified.
Compound (Z)-1b. 31P{1H} NMR (162 MHz, CDCl3) dZ
2
2
49.3 (d, JPPZ17.9 Hz) and 25.6 (d, JPPZ17.9 Hz).
4.1.3. 2,6-Bis(2-methylphenyl)-1,4-bis(2,4,6-tri-t-butyl-
phenyl)-1,4-diphospha-1,4-dihydrofulvene (1c). Com-
pound 6c (138.4 mg, 0.353 mmol) in THF (0.7 mL) was
converted to 1c, by a method similar to that of 1b, by using
0.070 mL of n-BuLi (1.54 M solution in hexane). The
residue was recrystallized from hexane to give 52.4 mg
(38% yield) of a mixture of (E)-1c and (Z)-1c.
4.1.1. 2,6-Diphenyl-1,4-bis(2,4,6-tri-t-butylphenyl)-1,4-
diphospha-1,4-dihydrofulvene (1a). To a solution of 6a
(182.7 mg, 0.483 mmol) in THF (1.0 mL) was added
0.075 mL of n-BuLi (1.60 M solution in hexane) at room
temperature and the resulting mixture was stirred overnight.
The solvent was removed under reduced pressure. Column
chromatography (SiO2) of the residue provided a mixture of
(E)-1a and (Z)-1a. To this mixture was added acetone and
insoluble (E)-1a3 was obtained (127.2 mg, 70% yield) by
filtration.
1
Compound (E)-1c. H NMR (600 MHz, CDCl3) dZ1.28
(18H, s, p-t-Bu), 1.59 (36H, br, o-t-Bu), 1.87 (3H, s, CH3),
3
2.56 (3H, s, CH3), 6.14 (1H, dd, JPHZ16.8 Hz, 7.2 Hz,
3
CHTol), 6.20 (1H, br d, arom.), 6.42 (1H, t, JHHZ7.5 Hz,
arom.), 6.48 (1H, dd, 2JPHZ36.9 Hz, 3JPHZ13.5 Hz, PCH),
3
3
6.76 (1H, t, JHHZ7.2 Hz, arom.), 6.84 (1H, d, JHH
Z
3
7.2 Hz, arom.), 6.96 (1H, t, JHHZ7.2 Hz, arom.0), 7.05
3
3
(1H, t, JHHZ7.5 Hz, arom.0), 7.18 (1H, d, JHHZ7.8 Hz,
Compound (Z)-1a. 31P{1H} NMR (162 MHz, CDCl3) dZ
3
arom.0), 7.36 (1H, d, JHHZ7.2 Hz, arom.0), 7.36 (2H, br,
2
2
m-Mes*), and 7.47 (2H, s, m-Mes*); 13C{1H} NMR
(151 MHz, CDCl3) dZ19.9 (s, CH3), 21.4 (s, CH3), 31.1
(s, p-CMe3), 31.3 (s, p-CMe3), 33.4 (br, o-CMe3), 33.9 (br,
o-CMe3), 34.7 (s, p-CMe3), 34.9 (s, p-CMe3), 39.4 (d,
48.9 (d, JPPZ19.5 Hz) and 25.2 (d, JPPZ19.5 Hz).
4.1.2. 2,6-Bis(4-methoxyphenyl)-1,4-bis(2,4,6-tri-t-butyl-
phenyl)-1,4-diphospha-1,4-dihydrofulvene (1b). To a
solution of 6b (122.4 mg, 0.300 mmol) in THF (0.6 mL)
was added 0.050 mL of n-BuLi (1.54 M solution in hexane)
at room temperature and the resulting mixture was stirred
overnight. The solvent was removed under reduced pressure
and a residual mixture of (E)-1b and (Z)-1b was obtained.
To the residue was added acetone and insoluble (E)-1b was
obtained (56.7 mg, 46% yield) by filtration.
3JPCZ3.0 Hz, o-CMe3), 39.5 (d, JPCZ3.0 Hz, o-CMe3),
3
123.4 (br, m-Mes*), 125.0 (s, Tol), 125.2 (s, Tol), 125.4 (s,
Tol), 125.7 (d, 4JPCZ9.1 Hz, Tol), 126.2 (s, Tol), 126.8 (d,
3
1JPCZ57.3 Hz, ipso-Mes*), 128.4 (dd, JPCZ7.5 Hz,
2
4JPCZ4.5 Hz, Tol), 129.0 (s, Tol), 131.0 (t, JPCZ7.5 Hz,
1
CHTol), 131.1 (s, Tol), 131.6 (d, JPCZ67.9 Hz, ipso-
1
2
Mes*), 131.6 (dd, JPCZ21.9 Hz, JPCZ11.3 Hz, PCH),

A. Nakamura et al. / Tetrahedron 61 (2005) 5223–5228
5227
1
3
134.7 (s, Tol), 134.9 (dd, JPCZ42.3 Hz, 30.2 Hz, PCP),
16.8 Hz, 6.0 Hz, CHPyr), 6.60 (1H, dd, JHHZ7.5 Hz,
135.5 (s, Tol), 136.3 (m, ipso-Tol), 138.7 (d, 2JPCZ21.1 Hz,
5.1 Hz, Pyr), 6.80 (1H, dd, JPHZ37.5 Hz, JPHZ12.3 Hz,
PCH), 6.99 (1H, dd, 3JHHZ7.5 Hz, 5.1 Hz, Pyr0), 7.25 (1H,
2 3
1
2
ipso-Tol), 141.3 (dd, JPCZ22.6 Hz, JPCZ15.1 Hz,
PCTol), 150.8 (s, p-Mes*), and 151.5 (s, o-Mes*);
3
d, JHHZ7.2 Hz, Pyr0), 7.41 (2H, s, m-Mes*), 7.49 (2H, s,
31P{1H} NMR (162 MHz, CDCl3) dZ64.1 (d, JPPZ
m-Mes*), 7.96 (1H, s, Pyr), 8.08 (1H, d, 3JHHZ4.2 Hz, Pyr),
2
26.6 Hz) and 24.2 (d, 2JPPZ26.6 Hz). HRMS [ESI, mixture
of (E)-1c and (Z)-1c]. Found m/z 784.5265. Calcd for
C54H74PC2 : MC, 784.5260.
8.34 (1H, d, JHHZ4.2 Hz, Pyr0), and 8.51 (1H, s, Pyr0);
3
13C{1H} NMR (151 MHz, CDCl3) dZ31.1 (s, p-CMe3),
31.2 (s, p-CMe3), 33.3 (br, o-CMe3), 33.9 (d, 4JPCZ4.5 Hz,
o-CMe3), 34.7 (s, p-CMe3), 34.9 (s, p-CMe3), 39.5 (d,
Compound (Z)-1c. 31P{1H} NMR (162 MHz, CDCl3) dZ
53.4 (d, JPPZ20.7 Hz) and 26.1 (d, JPPZ20.7 Hz).
3JPCZ4.5 Hz, o-CMe3), 39.6 (d, JPCZ4.5 Hz, o-CMe3),
3
2
2
122.7 (s, Py), 123.6 (br, m-Mes*), 124.1 (br, m-Mes*), 126.0
1
1
(d, JPCZ54.3 Hz, ipso-Mes*), 127.4 (d, JPCZ58.9 Hz,
1
2
ipso-Mes*), 128.0 (dd, JPCZ22.6 Hz, JPCZ10.6 Hz,
PCH), 129.7 (dd, JPCZ30.2 Hz, 22.6 Hz, CHPyr), 132.4
(dd, JPCZ7.5 Hz, 3.0 Hz, Pyr), 133.4–133.7 (m, ipso-Py),
133.5 (m, Py), 137.5 (dd, JPCZ41.5 Hz, 37.0 Hz, PCP),
4.1.4. 2,6-Bis(3-thienyl)-1,4-bis(2,4,6-tri-t-butylphenyl)-
1,4-diphospha-1,4-dihydrofulvene (1d). Compound 6d
(151.3 mg, 0.395 mmol) in THF (0.8 mL) was converted
to (E)-1d (78.0 mg, 52% yield), by a method similar to that
of 1b, by using 0.075 mL of n-BuLi (1.54 M solution in
hexane).
2
4
1
139.3 (t, JPCZ15.8 Hz, PCPyr), 145.8 (s, Py), 147.7 (t,
4
JPCZ3.0 Hz, Pyr), 147.8 (s, Py), 149.7 (t, JPCZ3.8 Hz,
Pyr), 151.4 (s, p-Mes*), 151.5 (s, p-Mes*), 152.4 (s,
o-Mes*), and 152.4 (s, o-Mes*); 31P{1H} NMR
Compound (E)-1d. Yellow solid, mp 203–205 8C
2
1
(162 MHz, CDCl3) dZ54.2 (d, JPPZ31.0 Hz) and 25.1
(decomp.); H NMR (600 MHz, CDCl3) dZ1.38 (9H, s,
p-t-Bu), 1.39 (9H, s, p-t-Bu), 1.63 (36H, br, o-t-Bu), 5.33
(d, 2JPPZ31.0 Hz); UV–Vis (hexane) 256 (log 3 4.59), 290
(sh, 4.38), and 419 nm (3.95); IR (KBr) n/cmK1 2960, 2906,
2868, 1591, 1527, 1473, 1398, 1360, 1238, 1209, 1182,
1124, 1024, 876, 791, and 708. HRMS (ESI). Found m/z
759.4926. Calcd for C50H68N2PC2 : MHC, 759.4930. Found:
C, 77.26; H, 8.99; N, 3.62%. Calcd for C50H68N2P2$H2O: C,
77.28; H, 9.08; N, 3.61%.
(1H, s, Thienyl), 6.04 (1H, s, Thienyl0), 6.45 (1H, d, 3JHH
Z
3
4.8 Hz, Thienyl), 6.73 (1H, dd, JPHZ17.7 Hz, 4.5 Hz,
CH,Thienyl), 6.76 (1H, dd, 2JPHZ37.8 Hz, 3JPHZ13.2 Hz,
PCH), 6.93 (1H, dd, 3JHHZ4.8 Hz, 4JHHZ2.4 Hz, Thienyl),
7.09–7.14 (2H, m, Thienyl0), 7.53 (2H, br, m-Mes*), and
7.56 (2H, br, m-Mes*); 13C{1H} NMR (151 MHz, CDCl3)
dZ31.2 (s, p-CMe3), 31.4 (s, p-CMe3), 33.4 (br, o-CMe3),
Compound (Z)-1e. 31P{1H} NMR (162 MHz, CDCl3) dZ
50.3 (d, JPPZ21.7 Hz) and 24.6 (d, JPPZ21.7 Hz).
4
33.9 (d, JPCZ4.5 Hz, o-CMe3), 34.8 (s, p-CMe3), 35.0 (s,
p-CMe3), 39.5 (d, JPCZ4.5 Hz, o-CMe3), 39.9 (br,
2
2
3
o-CMe3), 121.4 (t, JPCZ3.8 Hz, Thienyl), 121.5 (dd,
4JPCZ6.0 Hz, 4.5 Hz, Thienyl), 123.4 (s, Thienyl), 123.4
(br, m-Mes*), 124.2 (s, Thienyl), 125.5 (dd, 1JPCZ22.6 Hz,
2JPCZ10.6 Hz, PCH), 125.8 (d, JPCZ4.5 Hz, Thienyl),
127.5 (dd, 1JPCZ59.6 Hz, 3JPCZ2.3 Hz, ipso-Mes*), 128.3
(s, Thienyl), 129.2 (d, 1JPCZ63.4 Hz, ipso-Mes*), 129.3 (t,
4.1.6. 1,2-Bis(3-pyridyl)-3,4-bis[(2,4,6-tri-t-butylphenyl)-
phosphinidene]cyclobutene (3e). A mixture of (2,4,6-tri-t-
butylphenyl)phosphine (275.4 mg, 0.989 mmol) and AIBN
(10.3 mg, 0.0627 mmol) in CCl4 (3 mL) was refluxed for
4 h. The solvent was removed under reduced pressure and
2 mL of THF was added. In a separate flask, 1.01 mmol of
ethylmagnesium bromide (0.96 M solution in THF) was
added to a THF (2 mL) solution of 3-ethynylpyridine
(103.2 mg, 1.00 mmol) at 0 8C. The resulting solution was
stirred at 0 8C for 10 min., allowed to warm to room
temperature, and added to the THF solution of chloro(2,4,6-
tri-t-butylphenyl)phosphine prepared above. The resulting
mixture was stirred for 10 min and passed through short
silica-gel column using EtOAc as eluent. Removal of the
solvent afforded [(3-pyridyl)ethynyl]phosphine 6e, which
was used for the following reactions as obtained. To a
solution of 6e in THF (2 mL) was added 1.00 mmol of
n-BuLi (1.59 M solution in hexane) at K78 8C and the
resulting solution was stirred for 10 min, 1,2-dibromoethane
(0.0499 mmol) was added, and stirred for 10 min. The
resulting mixture was then allowed to warm to room
temperature and stirred for 1 h. The solvent was removed
under reduced pressure, 2 mL of toluene was added to the
residue, and the toluene solution was refluxed for 30 min.
Removal of the solvent under vacuum followed by column
chromatographic separation (SiO2/hexane–EtOAc)
provided 79.6 mg of 3e [21% based on the starting (2,4,6-
tri-t-butylphenyl)phosphine].
1
2JPCZ26.4 Hz, CH,Thienyl), 133.1 (dd, JPCZ41.5 Hz,
37.0 Hz, PCP), 137.2 (t, JPCZ11.3 Hz, PCThienyl), 138.9
2
3
(dd, JPCZ23.4 Hz, JPCZ2.3 Hz, ipso-Thienyl), 139.6 (d,
3JPCZ6.0 Hz, ipso-Thienyl), 151.3 (s, p-Mes*), 151.3 (s,
p-Mes*), 152.2 (s, o-Mes*), and 152.2 (s, o-Mes*); 31P{1H}
2
NMR (162 MHz, CDCl3) dZ48.0 (d, JPPZ24.9 Hz) and
19.7 (d, 2JPPZ24.9 Hz); UV–Vis (hexane) 255 (log 3 4.55),
285 (sh, 4.40), and 400 nm (3.92); IR (KBr) n/cmK1 2960,
2906, 2868, 1595, 1558, 1392, 1360, 1236, 1211, 1120, 874,
854, and 768. HRMS (ESI). Found m/z 768.4079. Calcd for
C48H66P2SC2 : MC, 768.4076.
Compound (Z)-1d. 31P{1H} NMR (162 MHz, CDCl3) dZ
2
2
46.6 (d, JPPZ15.2 Hz) and 23.8 (d, JPPZ15.2 Hz).
4.1.5. 2,6-Bis(3-pyridyl)-1,4-bis(2,4,6-tri-t-butylphenyl)-
1,4-diphospha-1,4-dihydrofulvene (1e). Compound 6e
(160.2 mg, 0.422 mmol) in THF (0.8 mL) was converted
to 1e (78.0 mg, 52% yield), by a method similar to that of
1b, by using 0.055 mL of n-BuLi (1.54 M solution in
hexane).
Compound (E)-1e. Yellow solid, mp 207–210 8C (decomp.);
1H NMR (600 MHz, CDCl3) dZ1.28 (9H, s, p-t-Bu), 1.29
(9H, s, p-t-Bu), 1.56 (18H, br, o-t-Bu), 1.59 (18H, br, o-t-
Yellow solid, mp 266–269 8C (decomp.); 1H NMR
(400 MHz, CDCl3) dZ1.37 (18H, s, p-t-Bu), 1.55 (36H,
Bu), 6.27 (1H, d, 3JHHZ7.8 Hz, Pyr), 6.36 (1H, dd, 3JPH
Z

5228
A. Nakamura et al. / Tetrahedron 61 (2005) 5223–5228
3
G. M.; Hufnagel, E. J. J. Chem. Soc., Chem. Commun. 1970,
1453.
´
2. For recent reviews, see: Segura, J. L.; Martın, N. Angew.
br, o-t-Bu), 6.50 (2H, d, JHHZ8.0 Hz, Pyr), 6.71 (2H, dd,
3JHHZ8.0 Hz, 4.8 Hz, Pyr), 7.33 (4H, s, m-Mes*), 7.86 (2H,
s, Pyr), and 8.22 (2H, d, 3JHHZ4.8 Hz, Pyr); 13C{1H} NMR
(100 MHz, CDCl3) dZ32.0 (s, p-CMe3), 33.7 (br, o-CMe3),
35.5 (s, p-CMe3), 38.7 (s, o-CMe3), 122.3 (s, arom.), 123.3
(s, arom.), 128.1 (s, arom.), 134.5 (pseudo t, JPCZ28.3 Hz,
ipso-Mes*), 135.2 (s, Pyr), 148.8 (s, arom.), 148.9 (s,
arom.), 151.1 (s, o-Mes*), 152.7 (pseudo t, JPCZ7.0 Hz,
PaC–C), 155.2 (s, o-Mes*), and 175.6 (dd, 1JPCZ18.4 Hz,
2JPCZ8.1 Hz, PZC); 31P{1H} NMR (162 MHz, CDCl3)
dZ179.6; UV–Vis (hexane) 246 (log 3 4.45), 325 (4.53),
and 377 nm (sh, 4.03); IR (KBr) n/cmK1 2954, 1591, 1471,
1400, 1363, and 1242. HRMS (ESI). Found m/z 757.4773.
Calcd for C50H67N2PC2 : MHC, 757.4774.
Chem. Int. Ed. 2001, 40, 1372. Bryce, M. R. J. Mater. Chem.
2000, 10, 589. Roncal, J. J. Mater. Chem. 1997, 7, 2307.
3. Ito, S.; Sekiguchi, S.; Yoshifuji, M. J. Org. Chem. 2004, 69,
4181.
4. (a) Appel, R.; Winkhaus, V.; Knoch, F. Chem. Ber. 1986, 119,
¨
2466. (b) Markl, G.; Reitinger, S. Tetrahedron Lett. 1988, 29,
463. (c) Yoshifuji, M.; Sasaki, S.; Inamoto, N. Tetrahedron
Lett. 1989, 30, 839.
5. Appel, R.; Winkhaus, V.; Knoch, F. Chem. Ber. 1987, 120,
243.
´
6. Cantat, T.; Mezailles, N.; Maigrot, N.; Richard, L.; Le Floch,
¨
P. Chem. Commun. 2004, 1274. Markl, G.; Weber, W.; Weib,
W. Chem. Ber. 1985, 118, 2365.
4.2. Reaction of 2ad with t-butyllithium
7. Arduengo, A. J., III; Harlow, R. L.; Kline, M. J. Am. Chem.
Soc. 1991, 113, 361. Arduengo, A. J., III. Acc. Chem. Res.
1999, 32, 913.
To a solution of 2ad (127.7 mg, 0.337 mmol, 97% D) in
THF (1.0 mL) was added 0.088 mmol (0.26 molar amount)
of t-BuLi (1.46 M solution in pentane) and the resulting
solution was stirred overnight. The solvent was evaporated
under reduced pressure. 31P NMR spectrum of the residue
showed signals due to (E)- and (Z)-diphosphadihydro-
fulvenes as well as the starting 2ad. To the residue was
added acetone and the insoluble (E)-1ad2 was obtained
(48.2 mg, 38% yield) by filtration. D content of the product
8. (a) Yoshifuji, M.; Toyota, K.; Murayama, M.; Yoshimura, H.;
Okamoto, A.; Hirotsu, K.; Nagase, S. Chem. Lett. 1990, 2195.
(b) Toyota, K.; Tashiro, K.; Abe, T.; Yoshifuji, M. Heteroat.
Chem. 1994, 5, 549. (c) Toyota, K.; Masaki, K.; Abe, T.;
Yoshifuji, M. Chem. Lett. 1995, 221. (d) Yamada, N.; Toyota,
K.; Yoshifuji, M. Chem. Lett. 2001, 248. (e) Yamada, N.; Abe,
K.; Toyota, K.; Yoshifuji, M. Org. Lett. 2002, 4, 569. (f)
Yoshifuji, M. Synth. Org. Chem. Jpn. 2003, 61, 1116 and
1
was determined by H NMR spectroscopy.
¨
references therein. See, also, (g) Markl, G.; Kreitmeier, P.;
¨
Noth, H.; Polborn, K. Angew. Chem., Int. Ed. Engl. 1990, 29,
¨
927. (h) Markl, G.; Hennig, R. Liebigs Ann. 1996, 2059.
Acknowledgements
9. (a) Yoshifuji, M.; Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi,
T. J. Am. Chem. Soc. 1981, 103, 4587. (b) Yoshifuji, M.;
Shima, I.; Inamoto, N.; Hirotsu, K.; Higuchi, T. J. Am. Chem.
Soc. 1982, 104, 6167. (c) Yoshifuji, M. J. Organomet. Chem.
2000, 611, 210. (d) Multiple Bonds and Low Coordination in
Phosphorus Chemistry; Regitz, M., Scherer, O. J., Eds.; Georg
Thieme: Stuttgart, 1990.
The authors thank Dr. Shigekazu Ito and Mr. Satoshi
Sekiguchi in these laboratories for valuable comments on
the structure determination of 1. This work was supported in
part by the Grants-in-Aid for Scientific Research (Nos
13304049, 14044012, 16033207, and 50217569) from the
Ministry of Education, Culture, Sports, Science, and
Technology, Japan.
10. A part of this work was presented at the 17th Symposium on
Fundamental Organic Chemistry, Sendai, September 2004,
Abstr. No. 2P003.
11. Yoshifuji, M.; Shibayama, K.; Inamoto, N.; Matsushita, T.;
Nishimoto, K. J. Am. Chem. Soc. 1983, 105, 2495.
References and notes
12. For preparation of 6a, see, Ref. 4b. For 6d, see: Toyota, K.;
Abe, K.; Horikawa, K.; Yoshifuji, M. Bull. Chem. Soc. Jpn.
2004, 77, 1377. Compounds 6b,c,e,f were prepared by the
analogous method and used after short silica-gel column.
1. Ferraris, J.; Cowan, D. O.; Walatka, V. V.; Perlstein, J. H.
J. Am. Chem. Soc. 1973, 95, 948. Coleman, L. B.; Cohen,
M. J.; Sandman, D. J.; Yamagishi, F. G.; Garito, A. F.; Heeger,
A. J. Solid State Commun. 1973, 12, 1125. Wudl, F.; Smith,
¨
13. Markl, G.; Kreitmeier, P. Angew. Chem., Int. Ed. Engl. 1988,
27, 1360.