P. Mastrorilli et al. / Tetrahedron Letters 47 (2006) 4759–4762
4761
Table 2.
were obtained with electron-withdrawing as well as
with electron-donating substituted aryldiazonium salts
(entries 4, 5 and 6 of Table 3 and entry 5 of Table 2).
A satisfactory 71% yield was achieved with the methyl
substituted diazonium ion (entry 7 of Table 3). The rela-
tive position of the substituent with respect to the diazo
group did not exert a remarkable effect on the reaction
course (entry 8 of Table 3 and entry 5 of Table 2).
Among the ortho substituted diazonium tetrachlorozinc-
ates, those bearing 2,5-(MeO)2C6H4 or 1-naphthyl gave
about 50% yield (entries 9 and 10), whereas the 2,4-di-
chlorophenyldiazonium salt afforded 68% yield (entry 11).
Entry
Chloride source
Time (h)
Yield (%)a
1
2
3
4
5
6
[bupy]Cl
[tba]Cl
[bmim]Cl
[bdmim]Cl
[dbim]Cl
[dbim]Clb
1
45
42
59
52
72
41
0.5
0.5
1.5
0.5
1
Reaction conditions: p-methoxyphenyldiazonium tetrachlorozincate
double salt: 2.50 mmol; methyl acrylate: 5.0 mL; azolium salt:
10 mmol; CuCl: 0.125 mmol; Zn dust: 0.250 mmol; room temperature.
[bupy] = butylpyridinium, [tba] = tetrabutylammonium, [bdmim] =
1,2-dimethyl-3-butylimidazolium, [dbim] = 1,3-dibutylimidazolium.
a GLC yield.
In conclusion, Meerwein reaction was successfully car-
ried out in ‘solventless’ conditions using a chloride based
ionic liquid. The catalytic system comprising of CuCl/
Zn in [bdim]Cl allowed to reach satisfactory (and repro-
ducible) results. Yields were fair even for electron-
donating substituted diazonium salts, which were noto-
riously poorly reactive in the Meerwein reaction.
b Without Zn and with 5 lL of water added to the reaction mixture.
Zn + Cu2+
Zn2+ + Cu0
2 Cu+
Cu2+ + Cu0
Scheme 3.
Acknowledgements
Cu(II) forming Cu(0) which reacts with residual Cu(II)
generating the active Cu(I) species (Scheme 3).
Polytechnic of Bari (F.R.A. funds) is gratefully acknow-
ledged for financial support.
The protocol based on bimetallic Zn/Cu catalyst and
[dbim]Cl was extended to other substrates (Scheme 4).
The results are listed in Table 3.
References and notes
The reactions were fast (completion was reached in less
than 30 min) and reproducible. The yields ranged from
49% to 71%. Activated olefins such as ethyl methacryl-
ate (entry 1), acrylonitrile (entry 2), and styrene (entry
3) gave yields of about 60%. The substituent on the aro-
matic core of aryldiazonium ions influenced the reaction
course,13 electron-donating groups generally decreasing
the yields. Interestingly, in our system comparable yields
1. Rondestvedt, C. S., Jr. Org. React. 1976, 24, 225–259.
2. Raucher, S.; Koolpe, G. A. J. Org. Chem. 1983, 48, 2066–
2069.
3. Theodoridis, G.; Malamas, P. J. Heterocycl. Chem. 1991,
28, 849–852.
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Yutaka, K. Chem. Pharm. Bull. 1983, 31, 560–569.
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8. Dickerman, S. C.; DeSouza, D.; Fryd, M.; Megna, I. S.;
Skoultchi, M. M. J. Org. Chem. 1969, 34(3), 714–719.
9. Dickerman, S. C.; Weiss, K.; Ingberman, A. K. J. Am.
Chem. Soc. 1958, 80, 1904–1911.
R
R
R'
CuCl/Zn
[dbim]Cl
Ar N2
ZnCl4
+
R'
2
Ar
Cl
Scheme 4.
10. Kochi, K. J. Am. Chem. Soc. 1957, 79, 2942–2948.
11. Kochi, K. J. Am. Chem. Soc. 1956, 78, 1228–1233.
12. Kochi, K. J. Am. Chem. Soc. 1955, 77, 5090–5092.
13. Doyle, M. P.; Siegfried, B.; Elliott, R. C.; Dellaria, J., Jr.
J. Org. Chem. 1977, 42, 2431–2436.
14. Obushak, N. D.; Lyakhovich, M. B.; Bilaya, E. E. Russ. J.
Org. Chem. 2002, 38, 38–46.
15. Ionic Liquids in Synthesis; Wasserscheid, P., Welton, T.,
Eds.; Wiley-VCH: Weinheim, 2003.
16. Wasserscheid, P. Transition Metal Catalysis in Ionic
Liquids; Wiley-VCH: Weinheim, 2003; pp 213–257.
17. Gallo, V.; Mastrorilli, P.; Nobile, C. F.; Paolillo, R.;
Taccardi, N. Eur. J. Inorg. Chem. 2005, 582–588.
18. Kabalka, G. W.; Dong, G.; Venkataiah, B. Tetrahedron
Lett. 2004, 45, 2775–2777.
Table 3. 23
Entry
Ar
R
R0
Yield (%)a
1
2
3
4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-NO2C6H4
p-COOEtC6H4
p-CH3CONHC6H4
p-CH3C6H4
m-MeOC6H4
2,5-(MeO)2C6H3
1-Naphthyl
COOEt
CN
Ph
Me
H
H
H
H
H
H
H
H
H
H
58
61
63
65
59
54
71
63
50
49
68
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
COOMe
5
624
7
8
9
10
11
2,4-Cl2C6H3
Reaction conditions: aryldiazonium tetrachlorozincate double salt:
2.50 mmol; olefin: 5.0 ml; [dbim]Cl: 10 mmol; CuCl: 0.125 mmol; Zn
dust: 0.250 mmol; reaction time: 30 min; room temperature.
a Isolated yield.
19. Laali, K. K.; Gettwert, V. J. J. Fluorine Chem. 2001, 107,
31–34.
20. Carmichael, A. J.; Haddleton, D. M.; Bon, S. A. F.;
Seddon, K. R. Chem. Commun. 2000, 1237–1238.