ence of potassium carbonate and rhodium(II) acetate dimer
catalyst leads to the intramolecular nitrene transfer, thereby
generating the corresponding aziridine in good to excellent
yields. However, this method would greatly benefit from the
use of a cheaper catalyst, such as copper complexes. In
this communication, we wish to report the use of pyridine
copper complexes for intra- and intermolecular alkene
aziridinations using N-tosyloxycarbamate reagents.
Table 1. Copper-Catalyzed Aziridination of
E)-5-Phenylpent-2-enyl N-Tosyloxycarbamate (eq 1)
(
3
,10
Sulfonyloxycarbamates are known to react with electron-
deficient alkenes via an AZA-Michael-initiated ring closing
entry
catalyst
yielda
1
2
3
4
5
6
7
8
9
none
<10%
(
AZA-MIRC) process to give the corresponding aziridines
b
Rh2(OAc)4
Cu(OTf)2
Cu(OTf)2‚Benzene
Cu(pyridine)2Cl2
Cu(pyridine)4(OTf)2
Cu(pyridine)4(OTf)2
Cu(pyridine)4(OTf)2
Cu(pyridine)2(BArF4)2e
Cu(pyridine)4(BF4)2
74%
45%
50%
53%
74%
84%
72%
82%
74%
8
in good yields. The reaction of such reagents with non-
activated alkenes (in the absence of catalyst) leads to low
yields and unselective processes typically observed with free
nitrenes.1c,11
Conversely, the use of the rhodium(II) acetate
c
dimer catalyst allowed the intramolecular aziridination of
d
9
allylic N-tosyloxycarbamates (Table 1, entries 1 and 2).
Copper complexes are known to promote aziridination of
10
3
alkenes in the presence of sulfonyliminoiodinane reagents.
a
Isolated yield by flash chromatography. b 7 equiv of K2CO3 was used,
see ref 9a. c 2 mol % of catalyst. d 1 mol % of catalyst. BAr 4 ) tetra[3,5-
e
F
(5) Transition metals other than Cu and Rh: (a) Breslow, R.; Gellman,
di(trifluoromethyl)phenyl]borate.
S. H. Chem. Commun. 1982, 1400-1401. (b) Groves, J. T.; Takahashi, T.
J. Am. Chem. Soc. 1983, 105, 2073-2074. (c) Mahy, J. P.; Battioni, P.;
Mansuy, D. J. Am. Chem. Soc. 1986, 108, 1079-1080. (d) Noda, K.;
Hosoya, N.; Irie, R.; Ito, Y.; Katsuki, T. Synlett 1993, 469-471. (e)
Nishikori, H.; Katsuki, T. Tetrahedron Lett. 1996, 37, 9245-9248. (f) Liang,
J. L.; Huang, J. S.; Yu, X. Q.; Zhu, N. Y.; Che, C. M. Chem. Eur. J. 2002,
However, the use of copper(II) triflate for the intramolecular
aziridination of allylic N-tosyloxycarbamates led to aziridi-
nation product 1 with only moderate yields (entries 3 and
8, 1563-1572. (g) Cui, Y.; He, C. J. Am. Chem. Soc. 2003, 125, 16202-
16203. (h) Li, Z. G.; Ding, X. Y.; He, C. J. Org. Chem. 2006, 71, 5876-
5880.
4
). We postulated that the solubility of the copper species
(
6) (a) Li, Z.; Conser, K. R.; Jacobsen, E. N. J. Am. Chem. Soc. 1993,
might be an issue, as the reaction between copper(II) triflate
and potassium carbonate could generate a very insoluble
copper carbonate species. We then studied the use of ligands
to make a more soluble species and to accelerate the reaction.
We chose to investigate pyridine copper complexes as these
are known to efficiently catalyze the aziridination of alkenes
1
15, 5326-5327. (b) Evans, D. A.; Faul, M. M.; Bilodeau, M. T.; Anderson,
B. A.; Barnes, D. M. J. Am. Chem. Soc. 1993, 115, 5328-5329. (c)
Jacobsen, E. N.; Li, Z.; Quan, R. W. J. Am. Chem. Soc. 1995, 117, 5889-
5
890. (d) Sanders, C. J.; Gillespie, K. M.; Bell, D.; Scott, P. J. Am. Chem.
Soc. 2000, 122, 7132-7133. (e) Fruit, C.; Robert-Peillard, F.; Bernardinelli,
G.; Muller, P.; Dodd, R. H.; Dauban, P. Tetrahedron: Asymmetry 2005,
1
6, 3484-3487. (f) Ma, L. G.; Jiao, P.; Zhang, Q. H.; Xu, J. X.
Tetrahedron: Asymmetry 2005, 16, 3718-3734. (g) Wang, X. S.; Ding,
3j
with PhINTs. However, we did not observed an improve-
K. L. Chem. Eur. J. 2006, 12, 4568-4575.
ment using Cu(pyridine)
2 2
Cl (entry 5). Conversely, com-
(7) For alternative methods, see: (a) Sharpless, K. B.; Jeong, J. U.; Tao,
B.; Sagasser, I.; Henniges, H. J. Am. Chem. Soc. 1998, 120, 6844-6845.
plexes containing less coordinating anionic ligands, such as
(
b) Bergmeier, S. C.; Stanchina, D. M. J. Org. Chem. 1999, 64, 2852-
1
2
F
triflate, tetra[3,5-di(trifluoromethyl)phenyl]borate (BAr
or tetrafluoroborate, led to the desired aziridine 1 with 74-
4% yields (entries 6, 8-10). However, no significant
difference was detected between the use of the more
4
),
2
5
9
859. (c) Chanda, B. M.; Vyas, R.; Landge, S. S. J. Mol. Catal. 2004, 223,
7-60. (d) Siu, T.; Picard, C. J.; Yudin, A. K. J. Org. Chem. 2005, 70,
32-937. (e) Catino, A. J.; Nichols, J. M.; Forslund, R. E.; Doyle, M. P.
8
Org. Lett. 2005, 7, 2787-2790. (f) Kawabata, H.; Omura, K.; Katsuki, T.
Tetrahedron Lett. 2006, 47, 1571-1574.
(8) AZA-MIRC: (a) Fazio, A.; Loreto, M. A.; Tardella, P. A. Tetra-
F
expensive BAr
4
over the triflate and the tetrafluoroborate
hedron Lett. 2001, 42, 2185-2187. (b) Fioravanti, S.; Morreale, A.;
Pellacani, L.; Tardella, P. A. Synthesis 2001, 1975-1978. (c) Fioravanti,
S.; Mascia, M. G.; Morreale, A.; Pellacani, L.; Tardella, P. A. Eur. J. Org.
Chem. 2002, 4071-4074. (d) Gasperi, T.; Loreto, M. A.; Tardella, P. A.;
Gambacorta, A. Tetrahedron Lett. 2002, 43, 3017-3020. (e) Fioravanti,
S.; Morreale, A.; Pellacani, L.; Tardella, P. A. J. Org. Chem. 2002, 67,
anionic ligand. Thus, the study was pursued with the triflate
complex. Not only are copper complexes cheaper than
rhodium complexes, but it was also possible to decrease the
catalyst loading of Cu(pyridine)
affecting the yield (entry 7). Optimization with Cu(pyridine)
OTf) showed that no yield improvement was observed
when changing either the solvent or the base.
A variety of allylic N-tosyloxycarbamates were then treated
with 2 mol % of Cu(pyridine) (OTf) in the presence of 5
4 2
(OTf) to 2 mol % without
4
972-4974. (f) Fioravanti, S.; Morreale, A.; Pellacani, L.; Tardella, P. A.
4
-
Eur. J. Org. Chem. 2003, 4549-4552. (g) Fioravanti, S.; Morreale, A.;
Pellacani, L.; Tardella, P. A. Synlett 2004, 1083-1085. (h) Mahoney, J.
M.; Smith, C. R.; Johnston, J. N. J. Am. Chem. Soc. 2005, 127, 1354-
(
2
1
355. (i) Shen, Y. M.; Zhao, M. X.; Xu, J. X.; Shi, Y. Angew. Chem., Int.
Ed. 2006, 45, 8005-8008. (j) Vesely, J.; Ibrahem, I.; Zhao, G. L.; Rios,
R.; C o´ rdova, A. Angew. Chem., Int. Ed. 2007, 46, 778-781.
4
2
(9) (a) Lebel, H.; Huard, K.; Lectard, S. J. Am. Chem. Soc. 2005, 127,
equiv of potassium carbonate in acetone. Under these reaction
conditions, the corresponding aziridine was isolated with a
good yield (Table 2). Aliphatic and aromatic E-disubstituted
alkenes reacted stereospecifically to produce trans-aziridines
with 66% and 51% yield, respectively (entries 1 and 2).
Conversely, the aziridination of Z-disubstituted allylic N-
1
4198-14199. (b) Lebel, H.; Leogane, O.; Huard, K.; Lectard, S. Pure
Appl. Chem. 2006, 78, 363-375. (c) Lebel, H.; Huard, K. Org. Lett. 2007,
, 639-642.
10) During the course of preparing this manuscript, Fleming and
9
(
coworkers reported the use of a copper(I) catalyst for the intramolecular
aziridination of allylic tosyloxycarbamates; see: Liu, R.; Herron, S. R.;
Fleming, S. A. J. Org. Chem. 2007, 72, 5587-5591.
(11) For examples, see: (a) Barani, M.; Fioravanti, S.; Pellacani, L.;
Tardella, P. A. Tetrahedron 1994, 50, 11235-11238. (b) Fioravanti,
S.; Luna, G.; Pellacani, L.; Tardella, P. A. Tetrahedron 1997, 53, 4779-
(12) Haynes, J. S.; Rettig, S. J.; Sams, J. R.; Trotter, J.; Thompson, R.
C. Inorg. Chem. 1988, 27, 1237-1241.
4
786.
4798
Org. Lett., Vol. 9, No. 23, 2007