7010
C. Huo et al. / Tetrahedron Letters 52 (2011) 7008–7010
by TBPAþꢀSbClꢁ6 . Single electron transfer between 1 and TBPAþꢀSbCl6ꢁ
produces the cation radical of the arylimine (1+Å) which is nucleo-
philic attacked by EDA, giving the cation radical adduct 5+Å. The lat-
ter undergoes ring closure by losing a nitrogen, giving the aziridine
cation radical 6+Å. This intermediate can subject to the second elec-
tron transfer with 1 to produce aziridine 2. The cation radical inter-
mediate 5+Å can also subject to 1,2-aryl migration followed by the
second electron transfer, giving enamine 3. The lack of formation
of the 1,2-hygrogen migration product which is frequently formed
in the Lewis acid-catalyzed azirination3f renders support to the cat-
ion radical mechanism. It is well-known that 1,2-hygrogen migra-
tion is impossible for free radical reactions.13
In concꢁlusion, we described that the triarylaminium salt
TBPAþꢀSbCl6 was an efficient initiator for the reaction between
chalcone epoxides and ethyl diazoacetate to construct aziridine
carboxylates with high cis-selectivity. The synthesis proceeds at
room temperature with low catalyst loading and without the
requirement of inert or anhydrous reaction conditions. We also
proposed a plausible cation radical mechanism that can explain
the form of the main product aziridine and the by-product.
Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991;
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10. Representative spectral data for the products: cis-1-(4-Chlorophenyl)-2-
carbethoxy-3-phenyl aziridine (2d): Colorless prisms, mp 122 °C. MS: m/z
301 (M+, 17), 228 (100); 1H NMR (300 MHz, CDCl3): d = 0.99 (t, J = 7.2 Hz, 3H,
CH3), 3.18 (d, J = 7.2 Hz, 1H, CHPh), 3.57 (d, J = 7.2 Hz, 1H, CHC@O), 3.94–4.10
(m, 2H, CH2), 7.00 (d, J = 8.4 Hz, 2H, Ar), 7.24 (d, J = 8.4 Hz, 2H, Ar), 7.29–7.50
(m, 5H, Ph). 13C NMR (100.08 MHz, CDCl3): d = 13.8, 45.7, 47.2, 61.1, 121.2,
127.5, 128.0, 128.1, 128.5, 129.1, 134.2, 151.0, 167.2.
Acknowledgments
We thank the National Natural Science Foundation of China
(21002080) and the Key project (210232) of the Education Minis-
try for financially supporting this work.
Ethyl 2-phenyl-3-(4-chloroanilino) acrylate (3d): Colorless oil. MS: m/z 301
(M+, 54), 105 (100). 1H NMR (300 MHz, CDCl3): d = 1.30 (t, J = 7.2 Hz, 3H, CH3),
4.26 (q, J = 7.2, 2H, CH2), 6.93 (d, J = 8.8 Hz, 2H, Ar), 7.27 (d, J = 8.8 Hz, 2H, Ar),
7.31 (d, J = 12.0 Hz, 1H, CH), 7.33–7.52 (m, 5H, Ph), 10.36 (d, J = 12.4 Hz, 1H,
NH). 13C NMR (100.08 MHz, CDCl3): d = 14.4, 60.0, 103.8, 116.7, 126.2, 128.0,
129.0, 129.5, 129.7, 137.6, 139.4, 143.2, 169.3.
References and notes
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