7208
Y. J. Kim, R. S. Varma / Tetrahedron Letters 45 (2004) 7205–7208
5. (a) Aghapoor, K.; Heravi, M. M.; Nooshabadi, M. A. Ind.
J. Chem. 1998, 37B, 84–86; (b) Khajavi, M. S.; Hajihadi,
M.; Nikpour, F. J. Chem. Res. 1996, 94–97.
and 2-amino-4-chlorophenol 12 gave the corresponding
2-benzoxazolone derivatives in good yields.
6. Bhanage, B. M.; Fujita, S.; Ikushima, Y.; Arai, M. Green
Chem. 2004, 6, 78–80.
In summary, a MW-assisted protocol for the direct syn-
thesis of cyclic urea has been developed that proceeds
expeditiously in the presence of ZnO. The reaction is
not only accelerated upon exposure to MW irradiation
thus shortening its reaction time but also eliminates
the formation of byproducts when compared to the tra-
ditional methods involving conventional heating.
7. (a) Gabriel, C.; Gabriel, S.; Grant, E. H.; Halstead, B. S.
J.; Mingos, D. M. P. Chem. Soc. Rev. 1998, 27, 213–230;
(b) Larhed, M.; Moberg, C.; Hallberg, A. Acc. Chem. Res.
2002, 35, 717; (c) Varma, R. S. Green Chem. 1999, 1, 43–
55; (d) Varma, R. S. Organic Synthesis Using Microwaves
and Supported Reagents. In Microwaves in Organic
Synthesis; Loupy, A., Ed.; Wiley-VCH: Weinheim, 2002,
p 181; (e) Varma, R. S. Advances in Green Chemistry:
Chemical Syntheses Using Microwave Irradiation; Astra-
Zeneca Research Foundation India, Bangalore, India,
8. The representative experimental procedure is as follows: A
mixture of urea (0.6g, 10mmol), ethylenediamine (0.6g,
10mmol), ZnO (0.06g, 0.73mmol), and DMF (1g) was
charged in a round-bottom glass flask containing a
magnetic stirring bar and fitted with a reflux condenser,
which was attached to a water aspirator for generating
reduced pressure to remove ammonia. The flask was
placed in a CEM Discover Focused Microwave Synthesis
System, which is designed to house a round-bottom flask
(50mL) containing a magnetic stirring bar. The flask was
subjected to MW irradiation at 120°C (power 150–250W)
for 10min. After the reaction is completed, the flask was
removed from the MW cavity and cooled to room
temperature. The crude reaction mixture was identified
by GC–MS qualitative analysis. Quantification of the
products was obtained from the peak area ratios of the
reactants based on urea and corresponding products.
These yields were verified by comparing with the isolated
yields obtained in some cases by the following procedure:
The reaction mixture was filtered to remove solid ZnO.
Adding acetone to the filtrate resulted in the precipitation
of imidazolidine-2-one 1a, followed by filtration and
washing with copious acetone afforded pure 1a. The dried
product 1a was weighed for quantitative analysis and
Acknowledgements
We wish to thank Tom Deinlein, Julius Enriquez, Albert
Foster and Amy Zhao for their assistance. This research
was performed while the author held a National
Research Council Research Associateship Award at
Clean Processes Branch, National Risk Management
Research Laboratory, U.S. Environmental Protection
Agency.
References and notes
1. Hodge, C. N.; Lam, P. Y. S.; Eyermann, C. J.; Jadhav, P.
K.; Ru, Y.; Fernandez, C. H.; De Lucca, G. V.; Chang, C.
H.; Kaltenbach, R. J. C.; Aldrich, P. E. J. Am. Chem. Soc.
1998, 120, 4570–4581.
2. (a) Bate, H. A.; Condulis, N.; Srein, N. L. J. Org. Chem.
1986, 51, 2228–2229; (b) Liu, P. S.; Marquetz, V. E.;
Driscoll, J. S.; Fuller, R. W. J. Med. Chem. 1981, 24, 662–
666; (c) Lien, E. J.; Kumler, W. D. J. Med. Chem. 1968,
11, 214–219; (d) Sherwood, P. W. J. Coat. Technol. 1982,
54, 61–64; (e) Kondo, T.; Kotachi, S.; Tsuji, Y.; Watan-
abe, Y.; Mitsudo, T. Organometallics 1997, 16, 2562–2570.
3. (a) Boon, W. R. J. Chem. Soc. 1947, 307; (b) Hayward, R.
J.; Meth-Cohn, O. J. Chem. Soc., Perkin Trans. 1 1975,
212–214; (c) Maclaren, J. A. Aust. J. Chem. 1977, 30, 455–
461.
1
further identified by H and 13C NMR in DMSO-d6.
9. Butler, A. R.; Hussain, I. J. Chem. Soc., Perkin Trans. 2
1981, 317–323.
10. The isolation of 60 was unsuccessful due to the formation
of oligomerized product during the reaction.
4. Qian, F.; McCusker, J. E.; Zhang, Y.; Main, A. D.;
Chlebowski, M.; Kokka, M.; McElwee-White, L. J. Org.
Chem. 2002, 67, 4086–4092.