Scheme 3
Table 2. Preparation of Alkenes 3 from the Reaction of 1, 2,
and As3Ph3
a
time
(h)
product
(trans:cis)b
yield of
3 (%)c
entry
Ar in 2
p-BrPh (2a )
1
2
3d
6
6
3a (100:0)
3b (100:0)
3d (100:0)
3d (100:0)
3c (100:0)
3e (100:0)
3f (100:0)
3g (100:0)
3h (100:0)
3i (100:0)
3j (100:0)
3k (100:0)
3l
60
64
59
70
57
62
64
45
39
41
65
67
35
p-NO2Ph (2b)
Ph (2d )
12
6
4
Ph (2d )
5
trans-PhCHdCH(2c)
2-furfuryl- (2e)
o-NO2Ph (2f)
p-CH3OPh (2g)
2,4-(CH3O)2 Ph (2h )
p-CH3Ph (2i)
p-CNPh (2j)
8
6
6
7
4
8
12
12
12
6
9
10
11
12
13
o-ClPh (2k )
p-CHOPh (2l)e
6
6
with slightly lower yields. Wilkinson’s catalyst, RhCl(PPh3)3,
was a much less efficient catalyst (Table 1, entry 6). The
solvent did not affect the reaction significantly (Table 1,
entries 3 and 4). When using more active triethylarsine
instead of triphenylarsine, similar results were obtained
(Table 1, entry 10).
a 1 mol % Rh2(OAc)4 was used as the catalyst, 1,4-dioxane as solvent,
and 15% BnNEt3Cl as the PTC. b Determined by NMR spectroscopy.
c Isolated yield. d Et3As was used. e trans,trans-1,4-Bis(2-phenyl-ethenyl)-
2,3,5,6-tetrafluoro-benzene 3l was formed in 35% yield, and the byproduct
4-(2-pentafluorophenyl-vinyl) benzaldehyde was formed in 16% yield.
Interestingly, under the same conditions, Ph3P did not give
the expected alkene (Table 1, entry 11); hydrazine 4 was
isolated in 70% yield, which came from the intermediate
phosphazine (Scheme 3).18
When TPPFe(III)Cl was used instead of Rh2(OAc)4, the
expected alkene was isolated in 55% yield; however, it gave
a low stereselectivity (E:Z ) 3.1:1) (Table 1, entry 12). Using
(EtO)3P to trap the carbenoid and TPPFe(III)Cl as the
catalyst, a low yield and stereoselectivity were observed
(Table 1, entry 13). We cannot account for this finding at
this time. The results are summarized in Table 1.
containing alkenes. The results are summarized in Table 2.
The yields of the reactions with electron-deficient aldehydes
(entries 2, 7, and 11) are higher than with electron-rich
aldehydes (Table 2, entries 8-10), which is consistent with
our speculation that electron-deficient aldehydes have better
reactivity in this reaction.
Encouraged by the above results, we decided to employ
the in situ tosylhydrazone salts in the catalytic cycle (Scheme
5). As a result, the yields of the alkenes were lower than
Scheme 5
Scheme 4
stepwise, but the stereoselectivity was unchanged (Table 3).
In summary, we described a novel and straightforward
method for the synthesis of pure trans pentafluorophenyl-
containing alkenes from aldehydes in moderate to good yields
in a one-pot reaction. The present strategy capitalizes on the
reaction of aldehydes with arsonium ylides. Moreover, this
Under the optimized reaction conditions (Scheme 4), a
series of aldehydes was used to prepare pentafluorophenyl-
(14) (a) Tewari, R. S.; Chaturvedi, S. C. Tetrahedron Lett. 1977, 43,
3843. For reviews on arsonium ylides, see: (b) Lloyd, D.; Gosney, I.;
Ormiston, R. A. Chem. Soc. ReV. 1987, 16, 45. (c) Huang, Y.; Sheng, Y.
AdV. Organomet. Chem. 1982, 20, 113. (d) Johnson, A. W. Ylide Chemistry;
Academic Press: New York, 1966.
(15) (a) Doyle, M. P.; Mckervey, M. A.; Ye, T. Modern Catalytic
Methods for Organic Synthesis with Diazo Compounds: From Cyclopro-
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K.; Alonso, E.; Hynd, G.; Lydon, K. M.; Palmer, M. J.; Procelloni, M.;
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(16) (a) Aggarwal, V. K.; Alonso, E.; Fang, G.; Ferrara, M.; Hynd,
G.; Procelloni, M. Angew. Chem., Int. Ed. 2001, 40, 1433. (b) Aggarwal,
V. K.; Harvey, J. N.; Richardson, J. J. Am. Chem. Soc. 2002, 124,
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1514. (d) Aggarwal, V. K.; Alonso, E.; Bae, I.; Hynd, G.; Lydon, K. M.;
Palmer, M. J.; Patel, M.; Procelloni, M.; Richardson, J.; Stenson, R. A.;
Studley, J. R.; Vasse, J.-L.; Winn, C. L. J. Am. Chem. Soc. 2003, 125,
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(17) Bamford, W. R.; Steven, T. S. J. Chem. Soc. 1952, 4735.
(18) Miyamoto, T.; Matsumoto, J. Chem. Pharm. Bull. 1988, 36, 1321.
Org. Lett., Vol. 6, No. 3, 2004
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