Regiodivergent approach to α- and β-(arylthio)alkenylphosphane oxides and sulfides: Aminophosphanes as synthetic auxiliaries

Article abstract of DOI:10.1055/s-0028-1087416

β-(Arylthio)ethenylphosphane oxides and sulfides are easily prepared by nucleophilic addition of thiophenols to the C≡C bond of the respective P,P-diphenyl-P-phenylethynyl P(V) derivatives. The regioisomeric α-(arylthio) analogues can be also prepared, st

Full text of DOI:10.1055/s-0028-1087416

3172
LETTER
Regiodivergent Approach to a- and b-(Arylthio)alkenylphosphane Oxides and
Sulfides: Aminophosphanes as Synthetic Auxiliaries
Approach to
a-
and
b
-(
a
A
rylthio)al
t
kenylp
e
hosphane
O
o
xides and SulfidesAlajarín,* Carmen López-Leonardo,* Rosalía Raja
Departamento de Química Organica, Facultad de Química, Universidad de Murcia, Campus de Espinardo, 30100 Murcia, Spain
Fax +34(968)364149; E-mail: alajarin@um.es
Received 30 June 2008
Ar
Abstract: b-(Arylthio)ethenylphosphane oxides and sulfides are
H
N
R3
R4
R1
R2
R1
R2
easily prepared by nucleophilic addition of thiophenols to the C≡C
bond of the respective P,P-diphenyl-P-phenylethynyl P(V) deriva-
tives. The regioisomeric a-(arylthio) analogues can be also pre-
pared, starting from the same activated alkynes, by sequential
nucleophilic addition of aminophosphanes and thiophenols. In these
latter cases, aminophosphanes, which are recovered at the end of the
processes, act just as synthetic auxiliaries for modulating the regio-
chemical outcome of the global thiophenol addition.
ArNHPR5
PR5
+
2
2
R3 R4
Scheme 1 b-Elimination of aminophosphane units in P-alkyl imi-
nophosphoranes
phane auxiliary, could be succesfully achieved. Such
synthetic strategy would allow the preparation of the alter-
native regioisomers to those derived from the direct addi-
tion of the same nucleophile.
Key words: alkynes, aminophosphanes, nucleophilic additions,
phosphorus, regioselectivity
Here we present the results obtained when aminophos-
phanes are utilized as synthetic auxiliaries in the addition
of thiophenols to the triple carbon–carbon bonds of P,P-
diphenyl-P-phenylethynylphosphane oxide 1 and sulfide
2 (Scheme 2).
A few examples of nucleophilic additions to the C≡C
bond of some classes of P-alkynyl derivatives, such as
phosphane oxides and sulfides, phosphonates, and thio-
phosphonates, have been described up to now.1 The regio-
chemical results of these reactions are in agreement with
the electron-withdrawing character of these P(V) func-
tionalities, which play the role of activating groups in such
processes.
ArSH
SAr
Ph2P
X
Ph
Ph
direct addition product
We have reported that aminophosphanes2 R1 PNHR2 are
2
Ph2P
X
excellent nucleophilic species in reactions with reactive
alkyl halides,3 and carbon–carbon double4 and triple5
bonds. In all these reactions the aminophosphanes experi-
ence regioselective alkylation at the P atom and, conse-
quently, they behave as synthetic equivalents of
SAr
1. Ph2PNHAr1
1 X = O
2 X = S
Ph
Ph2P
2. ArSH
X
– Ph2PNHAr1
indirect addition product
iminophosphide anions [R1 P=NR2]– or, in other words,
Scheme 2 Regiodivergent direct and indirect (by using aminophos-
phanes as synthetic auxiliaries) addition of thiophenols to alkynes 1
and 2
2
as iminophosphoranyl synthons. We have also shown that
Michael-type additions of nucleophiles to the C=C bond
of P-alkenyl iminophosphoranes are easy processes facil-
itated by the electron-withdrawing characteristics of the
iminophosphoranyl group.4,6 Additionally, we have re-
cently demonstrated that some P-alkyl iminophospho-
ranes bearing hydrogen atoms on the b-carbon atom may
easily experience b-elimination reactions of aminophos-
phane units (Scheme 1) yielding alkenes.5
We first tested the direct addition approach by reacting the
phosphane oxide 18 and sulfide 29 with thiophenols in the
presence of a catalytic amount (0.2 equiv) of potassium
hexamethyldisilazide (KHMDS), in toluene under reflux
for 12 hours, to give the b-(arylthio)ethenylphosphane ox-
ides 3 and sulfides 4, respectively (Scheme 3, Table 1).
These products were isolated as mixtures of Z- and E-
stereoisomers, and only in one case these two isomers
could be efficiently separated by chromatographic purifi-
cation on silica gel which was previously deactivated with
triethylamine (5% in hexane).10 As it has been found in
other nucleophilic additions to the C≡C bond of electron-
deficient alkynes,11 the reactions leading to 3 and 4 are to-
tally regioselective, the nucleophilic part of the reagents
adding to the carbon atom which is in the b-position to the
phosphorus atom.
On the basis of an adequate combination of these prece-
dents, we reasoned that aminophosphanes might be useful
synthetic auxiliaries7 in indirect additions of nucleophiles
to activated alkynes, as far as a three-step sequence con-
sisting of aminophosphane addition to the alkyne, further
addition of a nucleophile to the resulting P-alkenyl imino-
phosphorane, and final b-elimination of the aminophos-
SYNLETT 2008, No. 20, pp 3172–3176
1
6
.1
2
.2
0
0
8
Advanced online publication: 27.11.2008
DOI: 10.1055/s-0028-1087416; Art ID: D24108ST
© Georg Thieme Verlag Stuttgart · New York

LETTER
Approach to a- and b-(Arylthio)alkenylphosphane Oxides and Sulfides
3173
1H NMR spectra the value of 3JHP for the a-proton is close
to 21 Hz, coincident with other reports of cis 3JHP coupling
constants in P-vinyliminophosphoranes12 and analogous
bis(sulfides) and bis(oxides).13 In addition, in their 13C
NMR spectra, the quaternary ipso carbon of the C-phenyl
group appears coupled with phosphorus with a coupling
constant 3JCP = 8.4–8.9 Hz, which is in the typical range of
cis 3JCP values of comparable structures.13,14 The values of
the 3JPP coupling constants in their 31P NMR spectra, close
to 46 Hz, are in agreement with typical values found for
compounds bearing two P(V) atoms placed in relative
trans disposition of a carbon–carbon double bond.13b,15
Ph
KHMDS (0.2 equiv)
toluene, reflux, 12 h
Ph
SAr
3 X = O
4 X = S
+
ArSH
Ph2P
X
Ph2P
X
1 X = O
2 X = S
Scheme 3 Synthesis of b-(arylthio)ethenylphosphane oxides 3 and
sulfides 4
Table 1 b-(Arylthio)ethenylphosphane Oxides 3 and Sulfides 4
Product
X
Ar
Ratio Z/Ea Isolated yields (%)
Z-Isomer E-Isomer
Fortunately, the following two steps of the planned syn-
thetic strategy, namely the addition of thiophenols and the
further b-elimination of aminophosphane, occurred in a
single experimental step when species 6 and 7 were react-
ed with thiophenols in toluene at reflux, yielding the
a-(arylthio)ethenylphosphane oxides 8 and sulfides 9
(Scheme 5, Table 3).16
3a
3b
4a
4b
O
O
S
Tol
58:42
66:33
62:38
58:42
90b
51
PMP
Tol
25
75b
72b
S
PMP
a As determined by 1H NMR spectra of the final reaction mixtures.
b Global yield, Z- and E-isomers not separated.
Ar1
N
SAr2
PPh2
toluene, reflux, 24 h
We then approached the indirect addition route by reflux-
ing toluene solutions of the oxide 1 and sulfide 2 with a
number of aminophosphanes 5 for 24 hours in the pres-
ence of the same catalytic amount of KHMDS. The ex-
pected iminophosphoranyl phosphane oxides 6 and
sulfides 7 were, respectively, obtained in good yields
(Scheme 4, Table 2).12 It is worth noting that these nu-
cleophilic additions proceeded with total regio- and dia-
stereoselectivity, affording exclusively the E-isomers.
2
Ph2P
X
Ph2P
X
Ph
+
Ar SH
– Ph2PNHAr1
Ph
5
6 X = O
7 X = S
8 X = O
9 X = S
Ar1
N
H
Ar2S
PPh2
Ph2P
X
Ph
Scheme 5 Synthesis of a-(arylthio)ethenylphosphane oxides 8 and
sulfides 9.
Ar1
Ph2PNHAr1
Ph
N
α
Delightfully, these one-pot addition–elimination process-
es occur in a completely regioselective manner giving rise
to compounds 8 and 9 resulting from the introduction of
the ArS group at the a-carbon of the ethenyl fragment,
whereas the alternative regioisomers 3 and 4 were not de-
tected in the final reaction mixtures. This result is appar-
ently determined by the regiocontrol operating in the
thiophenol addition step, in which the P=N function con-
trols the conjugate addition whereas the P=X (X = O, S)
one is a mere spectator. This fact could be attributed to the
easy accessibility of the nucleophile to the less substituted
carbon atom of the C=C bond, as well as to the preactiva-
tion of the thiophenol by the interaction between its acidic
proton and the basic N center of the iminophosphoranyl
fragment.
5
PPh2
β
Ph2P
X
Ph2P
X
KHMDS (0.2 equiv)
toluene, reflux, 24 h
Ph
1 X = O
2 X = S
6 X = O
7 X = S
Scheme 4 Aminophosphane additions to alkynes 1 and 2
Table 2 (E)-b-(Iminophosphoranyl)phosphane Oxides 6 and Sul-
fides 7
Product
6a
X
O
O
O
S
Ar1
Isolated yields (%)
Tol
65
78
88
90
81
83
6b
PMP
6c
4-BrC6H4
Tol
Previously unknown a-(arylthio)ethenylphosphane ox-
ides 8 and sulfides 9 were so obtained in fair to good
yields (Table 3). Although we carried out the reaction of
each thiophenol with several, differently Ar1-substituted
reactants 6 or 7, we could not determine a general trend
concerning which Ar1 group would give rise to the best
yield of products. Whereas the detailed study of the stere-
ochemical course of these processes and its rational expla-
nation are out of the bounds of this synthetic publication,
it is worth noting that phosphane oxides 8 were obtained
7a
7b
S
PMP
7c
S
4-BrC6H4
Careful scrutiny of the NMR data of compounds 6 and 7,
paying particular attention to the values of the 3JHP, 3JCP,
and 3JPP coupling constants, allowed us the unambiguous
assignment of their E-geometries. For example, in their
Synlett 2008, No. 20, 3172–3176 © Thieme Stuttgart · New York

3174
M. Alajarín et al.
LETTER
Table 3 a-(Arylthio)ethenylphosphane Oxides 8 and Sulfides 9
Entry
Product
X
Ar1
Ar2
Ratio Z/Ea
Isolated yields (%)
Z-Isomer
80
E-Isomer
1
2
8a
8a
8a
8b
8b
8b
9a
9a
9a
9b
9b
9b
O
O
O
O
O
O
S
Tol
Tol
87:13
93:7
12
6
PMP
Tol
70
3
4-BrC6H4
Tol
Tol
74:26
58:42
58:42
57:43
100:0
100:0
100:0
100:0
100:0
100:0
68
25
32
24
39
-
4
PMP
PMP
PMP
Tol
44
5
PMP
43
6
4-BrC6H4
Tol
50
7
30
8
S
PMP
Tol
43
-
9
S
4-BrC6H4
Tol
Tol
56
-
10
11
12
S
PMP
PMP
PMP
58
-
S
PMP
37
-
S
4-BrC6H4
64
-
a As determined by integration in the 1H NMR spectra of the final reaction mixtures. Each isomer was unequivocally identified according to the
values of the 3JHP and 3JCP coupling constants shown by their b-H and phenyl C-ipso atoms, respectively, in the 1H NMR and 13C NMR spectra.
as mixtures of Z- and E-isomers, in which Z is always the amino-P,P-diphenylphosphane, the main products were
major component, with Z/E ratios ranging from 57:43 (en- also (Z)-8b/(E)-8b (66%, 77:23 ratio), although the con-
try 6) to 93:7 (entry 2). In contrast, phosphane sulfides 9 version was only 76%.
were isolated as single Z-isomers, although in lower
a-(Arylthio)alkenylphosphane oxides and sulfides have
yields. In the crude reaction mixtures leading to these lat-
been scarcely reported in the chemical literature. To our
ter compounds, we could detect phosphinothioic amides
knowledge, only the syntheses of 1-(phenylthio)vinyl-
Ar1NHP(S)Ph2 in variable amounts, that most probably
diphenylphosphane oxide, from its saturated analogue,18
are the result of a sulfur-atom transfer from sulfides 9 to
and (Z)-1-(phenylthio)crotyldiphenylphosphane oxide,
the aminophosphanes 5 originated in those reactions.
Such sulfur transfer, which has been shown to be feasible
from phosphorus atoms to more nucleophilic ones,17 can
account for the lower yields in sulfides 9 when compared
with oxides 8.
obtained from allyldiphenylphosphane oxide,19 have been
disclosed.
In summary, we have developed a convenient method for
modulating the regiochemistry of thiophenol additions to
the C≡C bond of P,P-diphenyl-P-phenylethynylphos-
phane oxide and sulfide, which allows the regiodivergent
approach to the a- and b-addition products. Whereas the
base-mediated addition of thiophenols led to the expected
b-(arylthio)ethenyl derivatives, the addition of amino-
phosphanes to the b-carbon of the alkyne, and its easy re-
moval after the further thiophenol addition are the key
points for the success of the indirect addition mode lead-
ing to the a-substituted products. We hope these results
may stimulate the search for new applications of amino-
phosphanes as auxiliary reagents in other addition reac-
tions.
We also attempted to carry out the indirect addition se-
quence in a one-pot manner. Thus, alkynylphosphane
oxide (1) was reacted with N-4-tolylamino-P,P-diphe-
nylphosphane (1 equiv) and KHMDS (0.2 equiv) in re-
fluxing toluene. After 24 hours, 4-methoxythiophenol (1
equiv) was added into the reaction flask and refluxing
continued for 12 hours. The 1H NMR and 31P NMR anal-
ysis showed that the major components of the final reac-
tion mixture were those resulting from the indirect
addition process [86% yield, (Z)-8b/(E)-8b = 87:13] al-
though accompanied by a minor amount of the direct
thiophenol addition isomers [14% yield, (Z)-3b/(E)-3b =
66:34].
Acknowledgment
Finally we tested a one-pot process in which the amino-
phosphane auxiliary was used in substoichiometric
amounts. When an equimolecular mixture of 1 and 4-
methoxythiophenol was refluxed in toluene solution for
24 hours in the presence of only 0.2 equiv of N-4-tolyl-
This work was supported by the MEC and FEDER (Project
CTQ2005-02323/BQU) and Fundación Séneca-CARM (Project
08661/PI/08). R. R. also thanks Universidad de Murcia for a fel-
lowship.
Synlett 2008, No. 20, 3172–3176 © Thieme Stuttgart · New York

LETTER
Approach to a- and b-(Arylthio)alkenylphosphane Oxides and Sulfides
3175
Hz, HAr), 6.99–7.11 (m, 3 H), 7.17–7.30 (m, 7 H), 7.37–7.50
(m, 5 H), 7.55 (d, 2 H, 3JHH = 9.0 Hz, HAr). 13C NMR (75
MHz, CDCl3): d = 55.53 (OCH3), 113.50 (d, 1JCP = 104.6
Hz, PCH=C), 115.51, 121.23 (quaternary), 128.10 (d,
3JCP = 12.1 Hz, Cm), 128.22, 129.23 (d, 4JCP = 1.2 Hz,),
129.39, 130.81 (d, 2JCP = 9.5 Hz, Co), 130.88 (d, 4JCP = 2.7
Hz, Cp), 133.69 (d, 1JCP = 106.6 Hz, Ci), 136.86 (d, 3JCP = 6.5
Hz, quaternary), 137.41, 161.12 (quaternary), 164.79 (d,
2JCP = 4.7 Hz, PCH=C). 31P NMR (121 MHz, CDCl3):
d = 17.90. MS (EI): m/z = 443 (11) [M + 1]+, 442 (28) [M]+,
201 (100). Anal. Calcd for C27H23O2PS (442.51): C, 73.28;
H, 5.24. Found: C, 73.39; H, 5.38.
References and Notes
(1) (a) Portnoy, N. A.; Morrow, C. J.; Chattha, M. S.; Williams,
J. C.; Aguiar, A. M. Jr. Tetrahedron Lett. 1971, 12, 1397.
(b) Maumy, M. Bull. Soc. Chim. Fr. 1972, 1600. (c) Märkl,
G.; Merkl, B. Tetrahedron Lett. 1983, 24, 5865.
(d) Kawashima, T.; Miki, Y.; Inamoto, N. Chem. Lett. 1986,
1883. (e) Lecerclé, D.; Sawacki, M.; Taran, F. Org. Lett.
2006, 8, 4283. (f) Huang, X.; Xu, L. Synthesis 2006, 231.
(g) Kondoh, A.; Yorimitsu, H.; Oshima, K. Org. Lett. 2008,
10, 3093.
(2) (a) Alajarín, M.; López-Leonardo, C.; Llamas-Lorente, P.
Top. Curr. Chem. 2005, 250, 77. (b) Alajarín, M.; López-
Leonardo, C.; Berná, J. In Science of Synthesis, Vol. 31;
Ramsden, C. A., Ed.; Thieme: Stuttgart, 2007, 1873.
(3) Alajarín, M.; López-Leonardo, C.; Llamas-Lorente, P.
Synlett 2003, 801.
(11) Dickstein, J. I.; Millar, S. I. In The Chemistry of the
Carbon–Carbon Triple Bond, Part 2; Patai, S., Ed.; Wiley:
Chichester, 1978, 813.
(12) Representative Experimental Procedure and Spectral
Data for Compounds 6
(4) Alajarín, M.; López-Leonardo, C.; Llamas-Lorente, P. Lett.
A solution of P,P-diphenyl-P-phenylethynylphosphane
oxide (1, 0.3 g, 1 mmol), P,P-diphenyl-P-(4-tolylamino)-
phosphane (0.44 g, 1.5 mmol), and KHMDS (0.5 M soln in
toluene, 0.4 mL, 0.2 mmol) in anhyd toluene (20 mL) was
refluxed for 24 h under a nitrogen atmosphere. Then, the
solvent was removed under reduced pressure, and the
residue was purified by chromatography on deactivated
silica gel (5% Et3N in hexane) with EtOAc–hexane 1:1 (v/v)
and then EtOAc to yield 6a as orange prisms (from CH2Cl2–
Et2O), mp 153–155 °C. IR (Nujol): 1505, 1439, 1331, 1181,
1119, 722, 706, 695 cm–1. 1H NMR (400 MHz, CDCl3):
d = 2.29 (s, 3 H, CH3), 6.82–6.86 (m, 6 H, HAr and Ph), 6.93–
6.99 (m, 3 H, HAr and Ph), 7.17–7.26 (m, 4 H, Ph2), 7.29–
7.45 (m, 12 H, Ph2), 7.63 (t, 1 H, 2JHP = 3JHP = 21.2 Hz, CH),
7.64–7.69 (m, 4 H, Ph2). 13C NMR (100 MHz, CDCl3):
d = 20.74 (CH3), 124.06 (d, 3JCP = 18.5 Hz, C2-Ar), 127.35,
128.06 (d, 5JCP = 1.2 Hz, C4-Ph), 128.26 (d, 3JCP = 12.1 Hz,
Cm), 128.47 (d, 3JCP = 12.1 Hz, Cm), 128.87 (d, 1JCP = 102.5
Hz, Ci), 129.55, 129.60, 130.77 (d, 2JCP = 9.7 Hz, Co),
131.30 (d, 4JCP = 2.7 Hz, Cp), 131.92 (d, 4JCP = 2.4 Hz, Cp),
132.80 (d, 2JCP = 9.2 Hz, Co), 133.12 (d, 1JCP = 105.4 Hz, Ci),
134.00 (t, 2JCP = 3JCP = 8.9 Hz, quaternary, C1-Ph), 137.90
[dd, 1JCP = 87.6 Hz, 2JCP = 5.4 Hz, PCH = CP], 147.97 (d,
2JCP = 2.0 Hz, quaternary, C1-Ar), 152.62 [d, 1JCP = 65.6 Hz,
PCH=CP], C4-Ar not observed. 31P NMR (121 MHz,
CDCl3): d = 4.39 (d, 3JPP = 45.4 Hz, P=N), 18.03 (d,
3JPP = 45.4 Hz, P=O). MS (EI): m/z = 594 (13) [M + 1]+, 593
(28) [M]+, 291 (100). Anal. Calcd for C39H33NOP2 (593.20):
C, 78.91; H, 5.60; N, 2.36. Found: C, 79.04; H, 5.46; N, 2.26.
(13) (a) Duncan, M.; Gallager, M. Org. Magn. Reson. 1981, 15,
37. (b) Sato, A.; Yorimitsu, H.; Oshima, K. Angew. Chem.
Int. Ed. 2005, 44, 1694.
Org. Chem. 2004, 1, 145.
(5) Alajarín, M.; López-Leonardo, C.; Llamas-Lorente, P.;
Raja, R. Tetrahedron Lett. 2007, 48, 6987.
(6) Alajarín, M.; López-Leonardo, C.; Llamas-Lorente, P.;
Bautista, D.; Jones, P. G. Dalton Trans. 2003, 426.
(7) (a) Katritzky, A. R.; Lan, X.; Yang, J. Z.; Denisko, O. V.
Chem. Rev. 1998, 98, 409. (b) Katritzky, A. R.; Rogovoy,
B. V. Chem. Eur. J. 2003, 9, 4586.
(8) Liu, B.; Wang, K.; Petersen, J. L. J. Org. Chem. 1996, 61,
8503.
(9) Issleib, K.; Harzfeld, G. Chem. Ber. 1962, 95, 268.
(10) Representative Experimental Procedure and Spectral
Data for Compounds 3
A solution of P,P-diphenyl-P-phenylethynylphosphane
oxide (1, 0.3 g, 1 mmol), 4-methoxythiophenol (0.21 g, 1.5
mmol), and KHMDS (0.5 M soln in toluene, 0.4 mL, 0.2
mmol) in toluene (20 mL) was refluxed for 12 h under a
nitrogen atmosphere. Then the solvent was removed under
reduced pressure, and the residue was purified by
chromatography on deactivated silica gel (5% Et3N in
hexane) with EtOAc–hexane 1:1 (v/v) and then EtOAc to
yield a mixture of Z- and E-isomers; Rf = 0.5 (EtOAc). The
subsequent fractional crystallization allowed the separation
of the two isomers.
(Z)-P,P-Diphenyl-P-[2-phenyl-2-(4-methoxyphenyl-
thio)]ethenylphosphane Oxide (Z-3b)
White needles (from CH2Cl2–Et2O), mp 196–197 °C. IR
(Nujol): 1589, 1544, 1491, 1439, 1246, 1181, 1119, 739,
719, 698 cm–1. 1H NMR (300 MHz, CDCl3): d = 3.63 (s,
3 H, OCH3), 6.51 (d, 2 H, 3JHH = 8.9 Hz, HAr), 6.53 (d, 1 H,
2JHP = 20.0 Hz, CHP), 6.88 (d, 2 H, 3JHH = 8.9 Hz, HAr),
7.16–7.19 (m, 3 H, Ph), 7.38–7.45 (m, 2 H, Ph), 7.46–7.51
(m, 6 H, Ph2), 7.87–7.94 (m, 4 H, Ph2). 13C NMR (75 MHz,
CDCl3): d = 55.08 (OCH3), 114.08, 122.41 (d, 1JCP = 104.5
Hz, PCH=C), 123.18 (quaternary), 128.04, 128.48, 128.50
(d, 3JCP = 12.2 Hz, Cm), 129.26, 131.19 (d, 2JCP = 9.8 Hz,
Co), 131.50 (d, 4JCP = 2.8 Hz, Cp), 134.35 (d, 1JCP = 106.7
Hz, Ci), 134.4, 139.03 (d, 3JCP = 14.4 Hz, quaternary),
159.20 (d, 2JCP = 1.0 Hz, PCH=C), 161.28 (quaternary).
31P NMR (121 MHz, CDCl3): d = 19.90. MS (EI): m/z = 443
(10) [M + 1]+, 442 (10) [M]+, 201 (100). Anal. Calcd for
C27H23O2PS (442.51): C, 73.28; H, 5.24. Found: C, 73.41; H,
5.10.
(14) Banert, K.; Fendel, W.; Schlott, J. Angew. Chem. Int. Ed.
1998, 37, 3289.
(15) (a) Colquhoun, I. J.; McFarlane, W. J. Chem. Soc., Dalton
Trans. 1982, 1915. (b) Schmidbaur, H.; Paschalidis, C.;
Steidelmann, O.; Wilkinson, D. L.; Müller, G. Chem. Ber.
1989, 1857. (c) Barnet, K.; Fendel, W.; Schlott, J. Angew.
Chem. Int. Ed. 1998, 37, 3289. (d) Tsuchii, K.; Nomoto, A.;
Ogawa, A. Tetrahedron Lett. 2006, 47, 3919.
(16) Representative Experimental Procedure and Spectral
Data for Compounds 8
A solution of 6a (0.78 g, 1.32 mmol) and 4-methoxythio-
phenol (0.21 g, 1.5 mmol) in anhyd toluene (20 mL) was
refluxed for 12 h under a nitrogen atmosphere. Then, the
solvent was removed under reduced pressure, and the
residue was purified by chromatography on deactivated
silica gel (5% Et3N in hexane) with EtOAc–hexane 1:1 (v/v)
and then EtOAc.
(E)-P,P-Diphenyl-P-[2-phenyl-2-(4-methoxyphenyl-
thio)]ethenylphosphane Oxide (E-3b)
White needles (from CH2Cl2), mp 119–120 °C. IR (Nujol):
1588, 1554 1492, 1439, 1247, 1176, 1167, 1116, 703, 691
cm–1. 1H NMR (300 MHz, CDCl3): d = 3.82 (s, 3 H, OCH3),
5.78 (d, 1 H, 2JHP = 15.2 Hz, CHP), 6.95 (d, 2 H, 3JHH = 9.0
Synlett 2008, No. 20, 3172–3176 © Thieme Stuttgart · New York

3176
M. Alajarín et al.
LETTER
(Z)-P,P-Diphenyl-P-[2-phenyl-1-(4-methylphenyl-
thio)]ethenylphosphane Oxide (Z-8b)
Rf = 0.55 (EtOAc); colourless oil. IR (Nujol): 1593, 1491,
1291, 1246, 1176, 1115, 722, 694 cm–1. 1H NMR (300 MHz,
CDCl3): d = 3.79 (s, 3 H, OCH3), 6.83 (d, 2 H, 3JHH = 8.8 Hz,
HAr), 7.01–7.03 (m, 3 H), 7.24 (d, 1 H, 3JHP = 48.2 Hz, CHP),
7.29–7.33 (m, 6 H, Ph2), 7.37–7.42 (m, 4 H, Ph), 7.72–7.77
(m, 4 H, Ph2). 13C NMR (75 MHz, CDCl3): d = 55.42
(OCH3), 115.19, 124.11 (d, 3JCP = 5.0 Hz, quaternary, C1-
Ar), 127.67, 128.07 (d, 3JCP = 12.2 Hz, Cm), 128.28, 129.73,
131.66 (d, 4JCP = 3.0 Hz, Cp), 131.92 (d, 2JCP = 9.3 Hz, Co),
131.97 (d, 1JCP = 89.8 Hz, PC=CH), 132.23 (d, 1JCP = 106.2
Hz, Ci), 135.12, 135.52 (d, 3JCP = 5.0 Hz, quaternary, C1-Ph),
146.26 (d, 2JCP = 7.4 Hz, PC=CH), 160.13 (quaternary).
31P NMR (121 MHz, CDCl3): d = 25.39. MS (EI): m/z = 442
(10) [M]+, 105 (100). Anal. Calcd for C27H23O2PS (442.51):
C, 73.28; H, 5.24. Found: C, 73.16; H, 5.32.
Rf = 0.7 (EtOAc); white prisms (from CH2Cl2–Et2O), mp
126–127 °C. IR (Nujol): 1589, 1493, 1434, 1298, 1246,
1201, 723, 694 cm–1. 1H NMR (400 MHz, CDCl3): d = 3.66
(s, 3 H, OCH3), 6.45 (d, 2 H, 3JHH = 8.9 Hz, HAr), 6.72 (d,
2 H, 3JHH = 8.9 Hz, HAr), 7.31–7.38 (m, 7 H, Ph2 and Ph),
7.44–7.47 (m, 2 H, Ph), 7.78–7.81 (m, 4 H, Ph2), 7.88–7.90
(m, 2 H, Ph), 8.27 (d, 1 H, 3JHP = 17.3 Hz, CHP). 13C NMR
(100 MHz, CDCl3): d = 55.26 (OCH3), 114.34, 124.63 (d,
3JCP = 1.5 Hz, quaternary, C1-Ar), 125.37 (d, 1JCP = 97.1 Hz,
PC=CH), 128.22 (d, 3JCP = 2.1 Hz, Cm), 128.38, 129.72,
130.25, 130.42 (dright, Ci), 130.77, 131.87 (d, 4JCP = 2.8 Hz,
Cp), 132.38 (d, 2JCP = 9.7 Hz, Co), 134.58 (d, 3JCP = 15.7 Hz,
quaternary, C1-Ph), 152.14 (d, 2JCP = 13.7 Hz, PC=CH),
158.25 (quaternary). 31P NMR (162 MHz, CDCl3):
d = 28.30. MS (EI): m/z = 443 (23) [M + 1]+, 442 (66) [M]+,
303 (100). Anal. Calcd for C27H23O2PS (442.51): C, 73.28;
H, 5.24. Found: C, 73.15; H, 5.32.
(17) Brown, D. H.; Cross, R. J.; Keat, R. J. Chem. Soc., Dalton
Trans. 1980, 871.
(18) Warren, S.; Zaslona, A. T. Tetrahedron. Lett. 1982, 23,
4167.
(E)-P,P-Diphenyl-P-[2-phenyl-2-(4-methoxyphenyl-
thio)]ethenylphosphane Oxide (E-8b)
(19) Grayson, J. I.; Warren, S.; Zaslona, A. T. J. Chem. Soc.,
Perkin Trans. 1 1987, 967.
Synlett 2008, No. 20, 3172–3176 © Thieme Stuttgart · New York

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