PPh3-catalyzed reactions of alkyl propiolates with N-tosylimines: A facile synthesis of alkyl 2-[aryl(tosylimino)methyl]acrylate and an insight into the reaction mechanism

Article abstract of DOI:10.1002/chem.200902105

A new PPh₃-catalyzed synthesis of alkyl 2-[aryl(tosylimino) methyl]acrylates from propiolate and N-tosylimine has been developed. Deuterium-labelling experiments show that the reaction mechanism involves several hydrogen-transfer processes, whi

Full text of DOI:10.1002/chem.200902105

DOI: 10.1002/chem.200902105
PPh3-Catalyzed Reactions of Alkyl Propiolates with N-Tosylimines:
A Facile Synthesis of Alkyl 2-[aryl(tosylimino)methyl]acrylate and
an Insight into the Reaction Mechanism
Huimin Liu, QiongMei Zhang, Limin Wang, and Xiaofeng Tong*[a]
Abstract: A new PPh3-catalyzed synthesis of alkyl 2-[aryl(tosylimino)methyl]acry-
lates from propiolate and N-tosylimine has been developed. Deuterium-labelling
experiments show that the reaction mechanism involves several hydrogen-transfer
processes, which are not the turnover-limiting step and strongly rely on the nature
of the reaction media. The stable phosphonium–enamine zwitterion, which was
proven to play an important role in the catalytic cycle, has been isolated and char-
acterised by X-ray analysis.
Keywords: hydrogen transfer
imines phosphanes reaction
mechanisms · zwitterions
·
·
·
Introduction
Much development in the chemistry of tertiary phosphanes
as nucleophilic catalysts has been achieved in the past few
decades.[1] This success might be ascribed to the properties
of tertiary phosphanes, such as strong nucleophilicity and
ease of ylide formation, as well as leaving group ability. The
combination of these unique properties allows tertiary phos-
phanes to perform 1,4-conjugate additions to a,b-unsaturat-
ed carbonyl compounds, to stabilise an adjacent carbanion
and to serve as an efficient leaving group. Furthermore, the
readily available variants of a,b-unsaturated carbonyl com-
pounds also provides this field with a large number of possi-
bilities for discovering new phosphane-catalyzed reactions.
In the case of the phosphane-catalyzed reactions of acti-
vated alkynes 1 with N-tosylimines 2, 1,3-zwitterions A are
Scheme 1. Reactivity of intermediate A as the nucleophile.
generally postulated to be versatile intermediates.[2] Reactiv-
ity strongly relies on the substituent R1 at the b position of
alkyne 1 (Scheme 1).[3] When R1 is an alkyl group, a [3+2]
cycloaddition reaction occurs to yield 3 (Scheme 1a).[4a] Al-
ternatively, the reaction pathway will be switched to pro-
duce compound 4 if the R1 group is a carboxylate (Sche-
me 1b).[4b] However, to the best of our knowledge, there has
been no success reported in the PR3-catalyzed reactions of
alkyl propiolates (R1 =H) with N-tosylimines.[5] Propiolates
have attracted increasing attention in the chemistry of C3-
homologation agents due to their versatile reactivity pro-
file.[6] Herein, we report a new PPh3-catalyzed reaction of
propiolate with N-tosylimine to give alkyl 2-[aryl(tosylimi-
no)methyl]acrylate (5) under simple conditions (Scheme 1c).
We also comprehensively investigated the reaction mecha-
nism and some significant details are disclosed.
[a] H. Liu, Q. Zhang, Prof. Dr. L. Wang, Dr. X. Tong
Key Laboratory for Advanced Materials and
Institute of Fine Chemicals
East China University of Science and Technology
Meilong Road 130, Shanghai, 200237 (P.R. China)
Fax : (+86)21-64253881
E-mail: tongxf@ecust.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902105.
1968
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1968 – 1972

FULL PAPER
Table 2. Reactions of 1 with 2 in the presence of PPh3 (20 mol%).[a]
Results and Discussion
When a mixture of methyl propiolate (1a) and phenyl tosy-
limine (2a) was treated with a catalytic amount of PPh3
(20 mol%) in toluene at room temperature for 24 h, the cor-
responding product 5aa was obtained in only 6% yield
(Table 1, entry 1). At elevated temperatures, there was no
Entry
R (1)
Ar (2)
Yield [%][b]
1[c]
2[c]
3
4
5
6
7
8
9
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Me (1a)
Bn (1b)
Bn (1b)
CH2CO2Et (1c)
Me (1a)
Ph (2a)
50 (5aa)
89 (5ab)
77 (5ac)
46 (5ad)
40 (5ae)
66 (5af)
55 (5ba)
80 (5bb)
62 (5cb)
0 (5ag)
4-MeO-C6H4 (2b)
4-Me-C6H4 (2c)
4-Br-C6H4 (2d)
4-Cl-C6H4 (2e)
piperonyl (2 f)
Ph (2a)
4-MeO-C6H4 (2b)
4-MeO-C6H4 (2b)
4-NO2-C6H4 (2g)
Table 1. Optimised conditions for the reaction between 1a and 2a in the
presence of PPh3 (20 mol%).[a]
10
[a] Reaction conditions: method B. For details see the Supporting Infor-
mation. [b] Yield of the isolated product. [c] The reaction was carried out
on a scale of 1a (7.2 mmol) and 2 (6 mmol) in toluene (60 mL).
Entry
1a [equiv]/[m][b]
Method
T [8C]
t [h]
Yield [%][c]
5aa
6
1
2
3
4
5
6
7
8
9
3.0/0.6
3.0/0.6
3.0/0.6
3.0/0.6
3.0/0.4
2.0/0.3
1.2/0.24
1.2/0.06
1.2/0.03
A
A
A
A
B
B
B
B
B
25
50
80
120
80
80
80
80
80
24
12
12
12
3
3
3
3
3
6
8
20
32
40
groups on the phenyl ring resulted in lower yields (Table 2,
entries 4 and 5). Especially, in the case of substrate 2g,
which has an NO2 group on the phenyl ring, no desired
product of 5ag was obtained (Table 2, entry 10) and (E)-
methyl 3-tosylacrylatein (7) was isolated in 6% yield in-
stead.
18
ND[d]
28
31
46
51
13
0
0
0
0
0
To better understand the mechanism of this transforma-
tion, we conducted the reaction with the deuterium-labelled
substrate [D]2b (Scheme 2). The deuterium atom was com-
[a] Reaction conditions: method A: 1a, 2a (1.0 mmol) and PPh3
(0.2 mmol) in toluene (5 mL) were mixed before the reaction was con-
ducted at the temperature indicated under N2; method B: the solution of
1a in toluene was slowly added to a mixture of 2a (1.0 mmol) and PPh3
(0.2 mmol) in toluene (10 mL) at 808C under N2 within 3 h. [b] [m]: con-
centration of 1a in toluene (molLÀ1). [c] Yield of the isolated product.
[d] ND=no product detected.
obvious improvement in the yield of 5aa (Table 1, entries 2–
4). However, compound 6, the dimer of 1a,[7] was obtained
in up to 40% yield in these cases (Table 1, entries 1–3). To
avoid the consumption of 1a through dimerisation, the solu-
tion of 1a in toluene was slowly added into the reaction
mixture of 2a and PPh3 over 3 h to maintain a low concen-
tration of 1a (Table 1, entry 5). Hence, the yield was in-
creased to 28%. A concentration of 0.06 molLÀ1 of 1a was
found to be optimum, with which 5aa could be obtained in
51% yield (Table 1, entry 8). The solvent was so crucial for
this transformation that other solvents, such as THF, ben-
zene, hexane, dioxane, DMSO, CH2Cl2 and CH3CN, led to
non-selective reactions with complete consumption of 2a.
With the optimised conditions in hand (Table 1, entry 8),
we directed our subsequent efforts towards testing the scope
of this reaction (Table 2). Besides 1a, (Table 2, entries 1–6),
both benzyl propiolate (1b) (Table 2, entries 7 and 8) and 2-
ethoxy-2-oxoethyl propiolate (1c) (Table 2, entry 9) can be
employed as substrates and deliver similar results. However,
other partners, namely, N-tosylimines 2a–g, impose more
significant electronic effects on this transformation. Higher
yields can be obtained when N-tosylimines 2 possess elec-
tron-donating groups on the phenyl ring (Table 2, entries 2
and 8), whereas N-tosylimines 2 with electron-deficient
Scheme 2. Reaction with deuterium-labelled substrate.
pletely incorporated into product [D]5ab at the b carbon
atom and was located in either the cis or trans position with
a ratio of 1:1 (see the Supporting Information for details).
On the basis of the results shown in Table 2 and
Scheme 2, a reaction mechanism is outlined in Scheme 3.
Scheme 3. Proposed mechanism.
Chem. Eur. J. 2010, 16, 1968 – 1972
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1969

X. Tong et al.
Addition of PPh3 to 1a forms the zwitterion A1, which un-
dergoes Mannich-type reaction with 2 to give the intermedi-
ate B. [1,2]-hydrogen transfer converts B to the intermediate
C. Then hydrogen transfer occurs again to provide the inter-
mediate D. Finally, [1,5]-elimination of PPh3 completes the
catalytic cycle and gives the product 5. Based on this pro-
posal, we might elucidate the important role of the aryl
group of N-tosylimines 2. The electron-rich aryl groups
might contribute significantly to the delocalisation of the b’
carbanion of C, which is thought to be a key step in the for-
mation of the intermediate D (Scheme 3, path a). On the
contrary, the aryl groups with electron-deficient groups
might, to some extent, stabilise this carbanion and prevent
the formation of the intermediate D. When a stronger elec-
tron-deficient group, such as NO2, is introduced, path a
(Scheme 3) will be completely shut down and the alternative
pathway (path b, Scheme 3) becomes the favourable route
to give anion 8, which will undergo further Michael addition
with 1a to produce compound (E)-methyl 3-tosylacrylate
(7) (Scheme 3).[8]
Scheme 5. Control experiment employing a 1:1:1 mixture of 2b, [D]2b
and 1a.
Scheme 6. Control experiment carried out in the presence of D2O.
with intramolecular pathway.[11] At present, we do not have
convincing evidence to clarify the reaction mechanism, but
the outcome of the reactions in Schemes 2, 4, 5 and 6
tempts us to discuss it (Scheme 7). Following the same reac-
tion pathway as that in Scheme 3, the interaction between
1a, 2a and PPh3 gives intermediate C1. Due to the ability of
PPh3 to stabilise an adjacent carbanion and the ease of for-
mation of the ylide, intermediate C may coexist with the
other two resonance forms E and F. In toluene, it is believed
that the intramolecular hydrogen-transfer process is fast and
5aa would be obtained without deuterium incorporation via
intermediate D1 (Scheme 7, path a). We presumed that ad-
ditional D2O would change the nature of the polarity of the
solvent systems. Therefore, the ion pairs of intermediate E
might be separated, to some extent, to facilitate the possibil-
ity of intermolecular reactions. Therefore, intermolecular
hydrogen transfer from D2O to E takes place to release one
equivalent of DOÀ and produce the deuterium-labelled in-
termediate G (Scheme 7, path b).[12] It is apparent that the
deuterium-labelled product [D]5aa could ultimately be ob-
tained via intermediates G and D2 (Scheme 7, path b).
We also carried out a series of control experiments to
obtain more mechanistic detail. Firstly, when a 1:1 mixture
of 2a (0.5 mmol) and [D]2b (0.5 mmol) was subjected to the
reaction conditions in the presence of 1a (1.2 mmol), no D–
H cross products were detected (Scheme 4). This result
Scheme 4. Control experiment with deuterated and non-deuterated sub-
strates.
strongly indicates that the hydrogen-transfer process occurs
intramolecularly. Secondly, when a 1:1:1 mixture of 2b
(0.5 mmol), [D]2b and 1a was employed (Scheme 5), it was
found that both 2b and [D]2b reacted at the same rate (kH/
kD =1.0) (see the Supporting Information). Thus, it can be
interpreted that the hydrogen-transfer process is not the
turnover-limiting step of the catalytic cycle.[9]
Moreover, the control experi-
To our surprise, only a trace of 5ca was observed by TLC
when the reaction of 1c and 2a was carried out in the pres-
ence of PPh3 (1 equiv) (Scheme 8). Fortunately, a dark-col-
oured solid was obtained after removal of the solvent. This
solid could be purified easily by recrystallisation in a mix-
ment was also conducted with
1a and 2a in the presence of
D2O (3 equiv) (Scheme 6). This
reaction was not hindered by
the presence of additional D2O
and smoothly proceeded to give
product 5aa in 58% yield.[10]
Note that 40% deuterium was
incorporated into the product
(Scheme 6). These results clear-
ly demonstrate that, in the pres-
ence of D2O, an intermolecular
pathway for the hydrogen-
transfer process exists, along Scheme 7. Different hydrogen-transfer pathways.
1970
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1968 – 1972

PPh3-Catalyzed Reactions of Alkyl Propiolates
FULL PAPER
zwitterions. These observations might show some common
characteristics of phosphane-catalyzed reactions.
Interestingly, the zwitterion 9ba was quite stable in tolu-
ene and did not decompose at all, even at 808C.[16] However,
when 1a (1 equiv) was added, zwitterion 9ba quickly de-
composed to yield PPh3 and 5ba (Scheme 9). Furthermore,
Scheme 8. Formation of the phosphonium–enamine zwitterions; Bn=
benzyl.
ture of CH2Cl2 and hexane. The structure was determined
and assigned as compound 9ca by spectroscopic data and X-
ray diffraction (Figure 1). Two other similar adducts, 9ab
and 9ba, can also be obtained under identical conditions.
Most notably, all of their 31P NMR spectra exhibited a diag-
nostic signal for tetravalent phosphorus at around d=
+22.0 ppm.[13] Clearly, these phosphorus atoms are identical
to that postulated in intermediate D in Scheme 3.
Scheme 9. Relationship between PPh3, 1, 5 and 9.
when a 1:1 mixture of 5ba and PPh3 in toluene was heated
at 808C for 3 h, the 31P NMR spectrum of the reaction mix-
ture exhibited only one signal, which could be assigned to
the zwitterion 9ba (Scheme 10). On the basis of these re-
Scheme 10. Balance between 9ba and 5ba.
sults, two important points can be concluded: 1) the zwitter-
ion 9 is qualified to be one intermediate for this catalytic re-
action; 2) elimination of PPh3 from the intermediate D is a
reversible step, but the balance is mainly shifted towards D
(Scheme 10). Thus, we assumed that the step in which PPh3
is eliminated from intermediate D would be a likely candi-
date for the turnover-limiting step of the catalytic cycle. Fur-
thermore, we believe that alkyl propiolates 1 not only work
as a reactant, but also as an efficient scavenger of PPh3
(Scheme 9): the reaction between propiolate and PPh3 might
ensure that the concentration of PPh3 would be reduced to a
very low level, which would destroy the balance of
Scheme 10 and facilitate the complete conversion of 9 to 5.
It is also believed to be the reason why intermediate 9 (in-
termediate D) could be isolated when equivalent amounts
of PPh3 and propiolates 1 were used (Scheme 8).
Figure 1. X-ray crystallography of 9ca. Ellipsoids at 30% probability.
The X-ray crystallographic data for 9ca (Figure 1) reveals
that the phosphorus atom has a tetrahedral geometry and
does not bond covalently with the nitrogen atom of the en-
À
amine–anion, as evidenced by the P1 N1 distance of
3.355 ꢁ (covalent radii of P and N are 1.05 and 0.68 ꢁ, re-
spectively). Importantly, this structure has long been postu-
lated as one of the key intermediates in aza-Baylis–Hillman
reactions.[14] Recently, Kwon et al. reported the first stable
phosphonium–enolate zwitterions, which have been un-
equivocally characterised by using X-ray crystallography.[15]
Slightly different from Kwonꢂs elegant work, PPh3 works
well in our research probably because of the introduction of
N-tosylimine as the electrophile. Therefore, we believe that
either electron-releasing alkyl substituents on the phospho-
nium centre or electron-withdrawing groups on the anion
centre play an important role in stabilising the phosphonium
Conclusion
A new PPh3-catalyzed reaction of alkyl propiolate with N-
tosylimine to give the adduct alkyl 2-[aryl(tosylimino)methy-
l]acrylate 5 has been developed. The proposed mechanism
involving the hydrogen-transfer process has been established
on the basis of a series of deuterium-labelling experiments.
It was found that the pathways of the hydrogen-transfer pro-
cess strongly depend on the nature of the reaction media.
Control experiments disclosed that the elimination of PPh3
Chem. Eur. J. 2010, 16, 1968 – 1972
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
1971

X. Tong et al.
Anary-Abbasinejad, Phosphorus, Sulfur Silicon Relat. Elem. 2002,
177, 81, and references therein.
[3] a) C. Zhang, X. Lu, J. Org. Chem. 1995, 60, 2906; b) C. Li, M. Shi,
Org. Lett. 2003, 5, 4273; c) K. Nozaki, N. Sato, K. Ikeda, H. Takaya,
J. Org. Chem. 1996, 61, 4516.
from the intermediate D can be assigned as the turnover-
limiting step of the catalytic cycle. Most importantly, we iso-
lated and characterised some stable phosphonium zwitter-
ions, which were found to be one of the key intermediates
in this new reaction. We believe that the highly activated
terminal olefin of 5 could be functionalised for further use
and the results will be reported in due course.[17] Efforts are
also underway to provide more mechanistic details and to
extend this study to new PPh3-catalyzed reactions.
[4] a) Z. Xu, X. Lu, J. Org. Chem. 1998, 63, 5031; b) L. Meng, P. Cai, Q.
Guo, S. Xue, J. Org. Chem. 2008, 73, 8491.
[5] a) G. Zhao, M. Shi, J. Org. Chem. 2005, 70, 9975; b) M. Shi, Y. Xu,
Chem. Commun. 2001, 1876; c) M. Shi, Y. Xu, J. Org. Chem. 2003,
68, 4784; d) G. L. Zhao, J. Huang, M. Shi, Org. Lett. 2003, 5, 4737.
[6] a) G. C. Hirst in Encyclopedia of Reagents for Organic Synthesis,
Vol. 5 (Ed.: L. A. Paquette), Wiley, New York, 1995, pp. 3576–3578;
b) J. Stowell, Chem. Rev. 1984, 84, 409; c) T. Nielsen, S. Schreiber,
Angew. Chem. 2008, 120, 52; Angew. Chem. Int. Ed. 2008, 47, 48;
d) D. Tejedor, S. Lopez-Tosco, F. Cruz-Acosta, G. Mendez-Abt, F.
Garcia-Tellado, Angew. Chem. 2009, 121, 2124; Angew. Chem. Int.
Ed. 2009, 48, 2090.
Experimental Section
General procedure for PPh3-catalyzed reactions: Compound 2a
(1.0 mmol) and PPh3 (52.4 mg, 20 mmol%) were added to toluene
(10 mL) in three-necked flask. The mixture was stirred at 808C under an
N2 atmosphere. A solution of 1a (1.2 mmol) in toluene (20 mL) was
slowly added to this reaction mixture within 3 h. Once the addition was
finished, the reaction mixture was cooled to room temperature. Then the
mixture was directly subjected to silica-gel column chromatography to
[7] Y. Matsuya, K. Hayashi, H. Nemoto, J. Am. Chem. Soc. 2003, 125,
646.
[8] a) N. Kamigata, H. Sawada, M. Kobayashi, J. Org. Chem. 1983, 48,
3793; b) F. A. Davis, R. L. Billmer, J. Org. Chem. 1985, 50, 2593;
c) D. Chen, X. Hou, L. Dai, J. Org. Chem. 2008, 73, 5578.
[9] This result is different from that of the Baylis–Hillman reaction in
which the hydrogen-transfer process is generally viewed as the turn-
over-limiting step; a) V. K. Aggarwal, S. Y. Fulford, G. C. Lloyd
Jones, Angew. Chem. 2005, 117, 1734; Angew. Chem. Int. Ed. 2005,
44, 1706; b) K. E. Price, S. J. Broadwater, B. J. Walker, D. T.
McQuade, J. Org. Chem. 2005, 70, 3980.
[10] a) V. K. Aggarwal, D. K. Dean, A. Mereu, R. Williams, J. Org.
Chem. 2002, 67, 510; b) J. Cai, Z. Zhou, G. Zhao, C. Tang, Org. Lett.
2002, 4, 4723; c) Y. M. A. Yamada, S. Ikegami, Tetrahedron Lett.
2000, 41, 2165; d) N. T. McDougal, S. E. Schaus, J. Am. Chem. Soc.
2003, 125, 12094; e) P. Buskens, J. Klankermayer, W. Leitner, J. Am.
Chem. Soc. 2005, 127, 16762, and references therein.
1
give the product 5aa. H NMR (400 MHz, CDCl3): d=7.91 (d, J=8.4 Hz,
2H), 7.89 (d, J=8.4 Hz, 2H), 7.57 (t, J=7.2 Hz, 1H), 7.43 (t, J=7.6 Hz,
2H), 7.35 (d, J=8. 4 Hz, 2H), 6.85 (s, 1H), 5.94 (s, 1H), 3.80 (s, 3H),
2.46 ppm (s, 3H); 13C NMR (100 MHz, CDCl3): d=173.6, 163.3, 144.0,
137.5, 137.0, 135.5, 134.0, 130.5, 129.7, 129.5, 128.7, 127.4, 52.4, 21.4 ppm;
MS (EI): m/z: 343 [M+]; HRMS: m/z calcd for C18H17NO4S: 343.3969,
found: 343.3971.
Acknowledgements
[11] a) Y. Xia, Y. Liang, Y. Chen, M. Wang, L. Jiao, F. Huang, S. Liu, Y.
Li, Z. Yu, J. Am. Chem. Soc. 2007, 129, 3470; b) E. Mercier, B. Fo-
novic, C. Henry, O. Kwon, T. Dudding, Tetrahedron Lett. 2007, 48,
3617.
Shanghai Municipal Committee of Science and Technology are greatly
appreciated (09ZR1408500). Special gratitude also goes to Prof. Xingyi
Wang and Dao Li for their long-term support.
[12] a) Y. Fang, E. N. Jacobsen, J. Am. Chem. Soc. 2008, 130, 5660; b) C.
Evans, S. J. Miller, J. Am. Chem. Soc. 2003, 125, 12394.
[1] For reviews, see: a) X. Lu, C. Zhang, Z. Xu, Acc. Chem. Res. 2001,
34, 535; b) X. Lu, Y. Du, C. Lu, Pure Appl. Chem. 2005, 77, 1985;
c) L. Ye, J. Zhou, Y. Tang, Chem. Soc. Rev. 2008, 37, 1140; d) J. L.
Methot, W. R. Roush, Adv. Synth. Catal. 2004, 346, 1035; e) D. Basa-
vaiah, A. J. Rao, T. Satyanarayana, Chem. Rev. 2003, 103, 811; f) V.
Nair, R. Menon, A. Sreekanth, N. Abhilash, A. Biju, Acc. Chem.
Res. 2006, 39, 520. Representative examples: g) S. A. Frank, D. J.
Mergott, W. R. Roush, J. Am. Chem. Soc. 2002, 124, 2404; h) L. C.
Wang, A. L. Luis, K. Agapiou, H. Jang, M. J. Krische, J. Am. Chem.
Soc. 2002, 124, 2402; i) C. E. Aroyan, S. J. Miller, J. Am. Chem. Soc.
2007, 129, 256; j) X. Zhu, J. Lan, O. Kwon, J. Am. Chem. Soc. 2003,
125, 4716; k) R. P. Wurz, G. C. Fu, J. Am. Chem. Soc. 2005, 127,
12234; l) M. E. Krafft, K. A. Seibert, T. F. N. Haxell, C. Hirosawa,
Chem. Commun. 2005, 5772; m) V. Nair, S. C. Mathew, A. T. Biju,
E. Suresh, Angew. Chem. 2007, 119, 2116; Angew. Chem. Int. Ed.
2007, 46, 2070; n) L. Ye, X. Sun, Q. Wang, Y. Tang, Angew. Chem.
2007, 119, 6055; Angew. Chem. Int. Ed. 2007, 46, 5951; o) Y. Du, X.
Lu, C. Zhang, Angew. Chem. 2003, 115, 1065; Angew. Chem. Int.
Ed. 2003, 42, 1035.
[13] a) C. Amatore, A. Jutand, M. MꢂBarki, G. Meyer, L. Mottier, Eur. J.
Inorg. Chem. 2001, 873; b) I. Yavari, F. Nourmohamm, Tetrahedron
2000, 56, 5221, and references therein.
[14] For reviews, see: a) G. Masson, C. Housseman, J. Zhu, Angew.
Chem. 2007, 119, 4698; Angew. Chem. Int. Ed. 2007, 46, 4614; b) V.
Declerck, J. Martinez, F. Lamaty, Chem. Rev. 2009, 109, 1.
[15] X. Zhu, C. Henry, O. Kwon, J. Am. Chem. Soc. 2007, 129, 6722.
[16] This reaction should be carried out under conditions strictly exclud-
ing O2, otherwise, Ph3P(O), probably oxidised by the residual O2,
would be detected in the 31P NMR spectrum of the reaction mixture.
Meanwhile, compound 5ba could be also obtained.
[17] The preliminary results of the application of 5 have been demon-
strated by the following two-step reaction in a one-pot procedure
(PCC=pyridinium chlorochromate):.
[2] a) D. E. C. Cobridge, Phosphorus: An Outline of Chemistry, Bio-
chemistry and Uses, 5th ed., Elsevier, Amsterdam, 1995; b) B. M.
Trost, G. Dake, J. Am. Chem. Soc. 1997, 119, 7595; c) C. Lu, X. Lu,
Org. Lett. 2002, 4, 4677; d) B. Liu, R. Davis, B. Joshi, D. W. Rey-
nolds, J. Org. Chem. 2002, 67, 4595; e) C. Larpent, G. Meignan, H.
Patin, Tetrahedron Lett. 1991, 32, 2615; f) I. Yavari, A. Alizadeh, M.
Received: July 29, 2009
Revised: October 30, 2009
Published online: December 23, 2009
1972
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 1968 – 1972