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R. S. Srivastava et al. / Tetrahedron Letters 52 (2011) 3478–3480
only single regioisomers. The reactivity and chemoselectivity fea-
tures of the reaction are comparable to the Mo-12, Fe-13,14 Cu(II)17
References and notes
,
and Cu(I) –catalyzed18–20 reactions reported earlier. However, the
product yield is much higher in the present case. The high yield
of reactions catalyzed by 1 compared to Cu(I) or Cu(II) alone can
be explained by the presence of both Cu(I) and Cu(II) with 1 from
the beginning to complete the redox cycle. On the other hand, a re-
dox couple is not available in the Cu(I)-catalyzed system at the
launch of the reaction and probably some hydroxylamine is re-
duced to ArNH2 by Cu(I), thus limiting the reaction yield.
1. Ricci, A. Modern Amination Reactions, Wiley-VCH, Weinheim, Germany, 2000.;
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To probe whether the Cu(I)/Cu(II)-catalyzed and Cu(I)-catalyzed
allylic aminations19,20 proceed via the same reaction pathway, we
employed the hetero Diels–Alder reaction of nitrosobenzene with
2,3-dimethylbutadiene as a trapping test for PhNO, a reactive eno-
phile that could account for the reactivity/selectivity features of
the aminations.21 The effective Diels–Alder trapping of PhNO by
2,3-dimethylbutadiene at 120 °C (bath temperature) in the pres-
ence of 2-methyl-2-pentene in dichloroethane was first estab-
lished (Scheme 1). When the amination reaction of 2-methyl-2-
pentene by phenyl hydroxylamine catalyzed by 1 (10 mol %) was
carried out in the presence of 2,3-dimethylbutadiene the allyl
amines derived from the alkene (major) and diene (minor), and a
trace amount of 3,4-dimethyl-N-phenylpyrrole were formed; the
Diels–Alder adduct (trapping product from PhNO) was not de-
tected (Scheme 1). In a separate experiment the D–A adduct was
shown to be stable under the catalytic conditions employed. Thus
both the Cu(I)/Cu(II)- and Cu(I)-only catalyzed reactions give the
same results, that is, no Diels–Alder adduct is formed. The results
further substantiate our earlier work,19,20 which argues against
the intermediacy of free PhNO in the catalysis by 1, and in support
of the involvement of Cu(I)/Cu(II) redox cycle. The mechanistic de-
tails can be found in our earlier work.19,20
6. (a) Kohmura, Y.; Kawasaki, K.-i.; Katsuki, T. Synlett 1997, 1456–1458; (b) Smith,
K.; Hupp, C. D.; Allen, K. L.; Slough, G. A. Organometallics 2005, 24, 1747–1755;
(c) Clark, J. S.; Roche, C. Chem. Commun. 2005, 5175–5177.
7. For other strategies for the amination of allylic and benzylic C–H bonds, see: (a)
Adam, W.; Krebs, O. Chem. Rev. 2003, 103, 4131–4146; (b) Johannsen, M.;
Jørgensen, K. A. Chem. Rev. 1998, 98, 1689–1708; Sharpless, K. B.; Hori, T. J. Org.
Chem. 1976, 41, 176; (c) Kresze, G.; Braxmeier, H.; Munsterer, H. Org. Synth.
1987, 65, 159; Katz, T. J.; Shi, S. J. Org. Chem. 1994, 59, 8297.
3. Conclusion
8. (a) Sharpless, K. B.; Hori, T.; Truesdale, L. K.; Dietrich, C. O. J. Am. Chem. Soc.
1976, 98, 269; (b) Bruncko, M.; Khuong, T. A. V.; Sharpless, K. B. Angew. Chem.,
Int. Ed. 1996, 35, 454.
9. Brimble, M. A.; Heathcock, C. H. J. Org. Chem. 1993, 58, 5261; Leblanc, Y.;
Zamboni, R.; Bernstein, M. A. J. Org. Chem. 1991, 56, 1971.
10. Keck, G. E.; Webb, R. R.; Yates, J. B. Tetrahedron 1981, 37, 4007; Knight, G. T.
Chem. Commun. 1970, 1016; Bank, R. E.; Hazeldine, R. N.; Miller, P. J.
Tetrahedron Lett. 1970, 4417.
11. Whitesell, J. K.; Yaser, H. K. J. Am. Chem. Soc. 1991, 113, 3526.
12. (a) Srivastava, A.; Ma, Y.; Pankayatselvan, R.; Dinges, W.; Nicholas, K. M. J.
Chem. Soc., Chem. Commun. 1992, 853; (b) Srivastava, R. S.; Nicholas, K. M. J.
Org. Chem. 1994, 59, 5365.
In conclusion, an equimolar mixture of Cu(I)/Cu(II), 1, catalyzes
the regioselective allylic amination of alkenes using hydroxyl-
amine as a nitrogen fragment donor in a much higher yield than
what was obtained when Cu(I) or Cu(II) was used. Furthermore,
the result substantiated our earlier findings, which argue against
the intermediacy of free PhNO in the catalysis by 1, and in support
of the involvement of Cu(I)/Cu(II) redox cycle.
4. Experimental section
13. (a) Srivastava, R. S.; Nicholas, K. M. Tetrahedron Lett. 1994, 35, 8739; (b)
Srivastava, R. S.; Khan, M. A.; Nicholas, K. M. J. Am. Chem. Soc. 1996, 118, 3311;
(c) Srivastava, R. S.; Nicholas, K. M. J. Am. Chem. Soc. 1997, 119, 3302; (d) Singh,
S.; Nicholas, K. M. Synth. Commun. 2001, 31, 3087.
4.1. Representative procedure for the amination of olefins by
aryl hydroxylamines catalyzed by CuCl/CuCl2
1
14. Johannsen, M.; Jorgensen, K. A. J. Org. Chem. 1994, 59, 214.
15. Srivastava, R. S.; Nicholas, K. M. Chem. Commun. 1998, 2705; Kolel-Veetil, M.;
Khan, M. A.; Nicholas, K. M. Organometallics 2000, 19, 3754; Srivastava, R. S.;
Nicholas, K. M. Tetrahedron Lett. 2002, 43, 931–934; Cenini, S.; Ragaini, F.;
Tollari, S.; Paone, D. J. Am. Chem. Soc. 1996, 118, 11964; Ragaini, F.; Cenini, S.;
Tollari, S.; Tummolillo, G.; Beltrami, R. Organometallics 1999, 18, 928.
16. Srivastava, R. S.; Nicholas, K. M. Chem. Commun. 1996, 2335.
17. Hogan, G. A.; Gallo, A. A.; Nicholas, K. M.; Srivastava, R. S. Tetrahedron Lett.
2002, 43, 9505.
A 1,2-dichloroethane (2 mL) solution of olefin (4.6 mmol) and
an equimolar mixture of anhydrous CuCl and CuCl2 1 (5 mol %
each) was refluxed (under N2/Ar).
A phenyl hydroxylamine
(0.75 mmol) solution in dichloroethane (8 mL) was delivered with
a syringe pump to the heated solution over a period of 5–6 h. After
cooling, the volatiles were removed under vacuum and the residue
was dissolved in diethyl ether. Column chromatography was car-
ried out on silica gel using dichloromethane/petroleum ether as
eluant to afford the N-aryl allylamines (Table 1). The allyl amines
were characterized by comparison of their spectroscopic data with
authentic samples as described in the literature.12–20
18. Ho, C.-M.; Lau, T.-C. New J. Chem. 2000, 24, 859.
19. Srivastava, R. S.; Tarver, N. R.; Nicholas, K. M. J. Am. Chem. Soc. 2007, 129, 15250.
20. Srivastava, R. S.; Tarver, N. R.; Nicholas, K. M. J. Am. Chem. Soc. 2005, 127, 7278.
21. Taylor, E. C.; Tseng, C.-P.; Rampal, J. B. J. Org. Chem. 1982, 47, 552.
Acknowledgments
We are grateful for financial support provided by the Louisiana
Board of Regents [LEQSF(2009-12)-RD-B-08].