Facile and Efficient Synthesis of Benzoxazoles and Benzimidazoles
Tucker, K. G. Watson, Bioorg. Med. Chem. Lett. 2005, 15,
2051–2055; e) M. S. Malamas, E. S. Manas, R. E. McDevitt, I.
Gunawan, Z. B. Xu, M. D. Collini, C. P. Miller, T. Dinh, R. A.
Henderson, J. C. Keith Jr., H. A. Harris, J. Med. Chem. 2004,
47, 5021–5040; f) H. Razavi, S. K. Palaninathan, E. T. Powers,
R. L. Wiseman, H. E. Purkey, N. N. Mohamedmohaideen, S.
Deechongkit, K. P. Chiang, M. T. A. Dendle, J. C. Sacchettini,
J. W. Kelly, Angew. Chem. Int. Ed. 2003, 42, 2758–2761.
a) B. E. Evans, K. E. Rittle, M. G. Bock, R. M. DiPardo,
R. M. Freidinger, W. L. Whitter, G. F. Lundell, D. F. Veber,
P. S. Anderson, R. S. L. Chang, V. J. Lotti, D. J. Cerino, T. B.
Chen, P. J. Kling, K. A. Kunkel, J. P. Springer, J. Hirshfield, J.
Med. Chem. 1988, 31, 2235–2246; b) D. A. Horton, G. T.
Bourne, M. L. Smythe, Chem. Rev. 2003, 103, 893–930 and ref-
erences cited therein.
a) M. Terashima, M. Ishii, Y. Kanaoka, Synthesis 1982, 484–
485; b) D. W. Hein, R. J. Alheim, J. J. Leavitt, J. Am. Chem.
Soc. 1957, 79, 427–429.
a) K. Bourgrin, A. Loupy, M. Soufiaoui, Tetrahedron 1998, 54,
8055–8064; b) R. S. Pottorf, N. K. Chadha, M. Katkevics, V.
Ozola, E. Suna, H. Ghane, T. Regberg, M. R. Player, Tetrahe-
dron Lett. 2003, 44, 175–178.
Various oxidants, such as DDQ, Mn(OAc)3, PhI(OAc)2, thian-
threne cation radical perchlorate, BaMnO4, NiO2, Pb(OAc)4,
and O2 with activated carbon, as well as MnO2/silica (under
microwave conditions, see ref.[4a]), have been used. For exam-
ples, see: a) J. Chang, K. Zha, J. Chang, K. Zhao, S. Pan, Tetra-
hedron Lett. 2002, 43, 951–954; b) R. S. Varma, D. Kumar, J.
Heterocycl. Chem. 1998, 35, 1539–1540; c) R. S. Varma, R. K.
Saini, O. Prakash, Tetrahedron Lett. 1997, 38, 2621–2622; d)
K. H. Park, K. Jun, S. R. Shin, S. W. Oh, Tetrahedron Lett.
1996, 37, 8869–8870; e) R. G. Srivastava, P. S. Venkataramani,
Synth. Commun. 1988, 18, 1537–1544; f) K. Nakagawa, H.
Onoue, J. Sugita, Chem. Pharm. Bull. 1964, 12, 1135–1138; g)
F. F. Stephens, J. D. Bower, J. Chem. Soc. 1949, 2971–2972; h)
Y. Kawashita, N. Nakamichi, H. Kawabata, M. Hayashi, Org.
Lett. 2003, 5, 3713–3715.
a) B. Yadagiri, J. W. Lown, Synth. Commun. 1990, 20, 955–963;
b) Q. Sun, B. Yan, Bioorg. Med. Chem. Lett. 1998, 8, 361–364;
c) P. N. Preston in The Chemistry of Heterocyclic Compounds
(Eds.: A. Weissberger, E. C. Taylor) Wiley, New York, 1981,
vol. 40, part 1, pp. 6–60; d) M. R. Grimmett in Comprehensive
Heterocyclic Chemistry (Eds.: A. R. Katritzky, C. W. Rees), Per-
gamon, Oxford, 1984, vol. pp. 457–487; e) T. Benincori, F. San-
nicolò, J. Heterocycl. Chem. 1988, 25, 1029–1033; f) J. G.
Smith, I. Ho, Tetrahedron Lett. 1971, 12, 3541–3542; g) R. Wei-
denhagen, Ber. Dtsch. Chem. Ges. 1936, 69, 2263–2272; h) see
ref.[5g]; i) S. Kumar, K. K. Kapoor, Synlett 2007, 2809–2814.
a) H. Q. Do, O. Daugulis, J. Am. Chem. Soc. 2007, 129, 12404–
12405; b) G. L. Turner, J. A. Morris, M. F. Greaney, Angew.
Chem. Int. Ed. 2007, 46, 7996–8000; c) B. Sezen, D. Sames,
Org. Lett. 2003, 5, 3607–3610.
a) D. G. Saunders, J. Chem. Soc. C 1969, 12, 680–680; b)
Y. A. M. Marghlani, S. A. M. Metwally, A. M. Mahmoud,
A. M. Osman, Pak. J. Sci. Ind. Res. 1980, 23, 166–168; c) T.
Fonseca, B. Gigante, T. L. Gilchrist, Tetrahedron 2001, 57,
1793–1799; d) A. Alberti, P. Carloni, L. Greci, P. Stipa, R.
Andruzzi, G. Marrosu, A. Trazza, J. Chem. Soc. Perkin Trans.
2 1991, 7, 1019–1023; e) H. C. Waterman, D. L. Vivian, J. Org.
Chem. 1949, 14, 289–297.
a) X.-Q. Zhu, H.-Y. Wang, J.-S. Wang, Y.-C. Liu, J. Org. Chem.
2001, 66, 344–347; b) J. Zhang, M.-Z. Jin, W. Zhang, L. Yang,
Z.-L. Liu, Tetrahedron Lett. 2002, 43, 9687–9689; c) S. J. Gar-
den, C. R. W. Guimaraes, M. B. Correa, C. A. F. de Oliveira,
A. D. Pinto, R. B. de Alencastro, J. Org. Chem. 2003, 68, 8815–
8822; d) Z. G. Zhang, P. R. Schreiner, Synthesis 2007, 2559–
2564 and references cited therein.
by Pd/C causes the formation of palladium hydride, which
can generate hydrogen if it is not captured by 1a. The re-
duction of 1a could lead to the formation of 2-aminophenyl
benzoate. The amine can undergo intramolecular cycliza-
tion to give dihydrobenzoxazol-2-ol, which loses a water
molecule in the presence of acetic acid to produce desired
product 2a.
[2]
Conclusions
In summary, a mild and efficient method for the synthe-
sis of benzo-fused azoles has been developed by using
Hantzsch ester 1,4-dihydropyridine (HEH) as a biomimetic
reducing agent. To the best of our knowledge, the reported
procedure represents the first application of the model com-
pound of coenzyme NAD(P)H in the synthesis of benzo-
fused azoles. Extension of this method to other potential
substrates is in progress in our laboratory.
[3]
[4]
[5]
Experimental Section
General: 1H and 13C NMR spectra were recorded with a Varian
instrument (300 and 75 MHz, respectively) or a Bruker instrument
(400 and 100 MHz, respectively) and internally referenced to the
tetramethylsilane signal or residual protio solvent signals. Mass
spectra were recorded by EI methods, and IR spectra were recorded
with a Nicolet NEXUS 670 FTIR spectrometer. HRMS data were
determined with a Bruker Daltonics APEXII 47e FTICR spec-
trometer. All reactions under standard conditions were monitored
by thin-layer chromatography (TLC) on gel F254 plates. Silica gel
(200–300 mesh) was used for column chromatography. The em-
ployed solvents were dried by the standard procedures. Commer-
cially obtained reagents were used without further purification.
[6]
General Procedure for the Synthesis of Benzo-Fused Azoles: To a
stirred solution of 1a–o or 2a–h (1.0 mmol) in acetic acid (20 mL)
was added HEH (3.6 mmol) and 10% Pd/C (2 wt.-% of HEH), and
the reaction mixture was heated at reflux for 15 h under an atmo-
sphere of N2. Then the mixture was filtered through Celite, and the
filtrate was evaporated in vacuo. The residue was purified by col-
umn chromatography on silica gel to give the corresponding prod-
uct.
[7]
[8]
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details and copies of the 1H and 13C NMR spec-
tra.
Acknowledgments
We thank the National Natural Science Foundation of China
(Grant No. 20702023) and the Special Fund for Doctoral Program
from the Ministry of Education of China (Grant No. 20070730040)
for financial support.
[9]
[1] a) M. O. Chaney, P. V. Demarco, N. D. Jones, J. L. Occolowitz,
J. Am. Chem. Soc. 1974, 96, 1932–1933; b) T. Kusumi, T. Ooi,
M. R. Walchli, H. Kakisawa, J. Am. Chem. Soc. 1988, 110,
2954–2958; c) A. D. Rodriguez, C. Ramirez, I. I. Rodriguez,
E. Gonzalez, Org. Lett. 1999, 1, 527–530; d) R. N. Brown, R.
Cameron, D. K. Chalmers, S. Hamilton, A. Luttick, G. Y.
Krippner, D. B. McConnell, R. Nearn, P. C. Stanislawski, S. P.
[10]
a) G. Barbe, A. B. Charette, J. Am. Chem. Soc. 2008, 130, 18–
19; b) S. G. Ouellet, A. M. Walji, D. W. C. Macmillan, Acc.
Chem. Res. 2007, 40, 1327–1339; c) N. J. A. Martin, X. Cheng,
Eur. J. Org. Chem. 2010, 6627–6632
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
6631