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of C(2)–C(3) double bond of the allenoates toward C–C–S
1,3-diploar components was remarkable and intriguing.
The 1,3-dipolar cycloadditions of various dipoles, such as
nitrones, diazoalkanes, and nitrile oxide, with electron-defi-
cient allenes have been investigated.42–46 According to the
literature, in most reactions, it was the activated C(1)–
C(2) double bond that underwent 1,3-dipolar cycloaddition
reaction, since the electron-withdrawing group caused low-
ering of the LUMO energy level of allenes, which favored
the dipole HOMO–dipolarophile LUMO interaction. Our
recent study also indicated that dipoles 9 preferred to react
with more electron-deficient dipolarophiles.30 However, we
now observed an opposite selectivity of the relatively less
activated C(2)–C(3) bond of allenoates in the C–C–S cyclo-
addition reaction. The exact reason for the reversed double
bond selectivity remains unclear at this stage, although we
may ascribe it to the formation of more stable conjugated
product. The stereoselective formation of Z-configured iso-
mer of 5 and E-configured isomer of 7 was most probably
due to the thermodynamic factors, as the substituents on
the double bond and on the thiophene or pyrrole ring tend
to keep far away to avoid steric strains.
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reospecific manner to produce predominantly spiro[benz-
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reaction was proposed via a tandem nucleophilic addition
of carbenes to isothiocyanates followed by an unusual
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double bond of allenoates. The novel spiro products are
not easily prepared by other synthetic methods and are
potentially amenable to further transformations. The
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Acknowledgments
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This work was supported by the National Natural Sci-
ence Foundation of China for Distinguished Young Schol-
ars (No. 20525207) and National Natural Science
Foundation of China (20672013).
Supplementary data
39. Gompper, R.; Wolf, U. Liebigs Ann. Chem. 1979, 1406.
40. Spectral data of selected compound: (Z)-Methyl 1,3-diethyl-20-ben-
zylimino-40-benzylspiro[benzimidazoline-2,30-tetrahydrothien-50-yli-
dene]acetate 5c: 42%, mp 119–120 °C; IR m (cmꢀ1) 1704, 1654, 1616,
1506; 1H NMR (500 MHz, CDCl3) d (ppm) 7.29–7.34 (m, 5H), 7.22–
7.27 (m, 5H), 6.61 (t, J = 4.1 Hz, 2H), 6.31 (dd, J = 6.0, 4.0 Hz, 1H),
6.28 (dd, J = 6.0, 4.0 Hz, 1H), 6.13 (d, J = 2.5 Hz, 1H), 4.64 (d,
J = 16.0 Hz, 1H), 4.60 (d, J = 16.0 Hz, 1H), 3.76 (s, 3H), 3.51 (d,
J = 15.9 Hz, 1H), 3.44 (d, J = 9.1 Hz, 1H), 3.32–3.40 (m, 2H), 3.11–
3.18 (m, 1H), 3.01–3.07 (m, 1H), 2.96 (dd, J = 16.0, 9.1 Hz, 1H), 1.11–
1.15 (m, 6H); 13C NMR (125 MHz, CDCl3) d (ppm) 166.5, 163.2,
158.1, 140.6, 139.3, 138.8, 138.5, 128.8, 128.3, 128.1, 127.6, 126.9,
Supplementary data associated with this article can be
References and notes
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1. Multicomponent Reactions; Zhu, J., Bienayme, H., Eds.; Wiley-VCH:
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