1304
D. J. Maher, S. J. Connon /Tetrahedron Letters 45 (2004) 1301–1305
Cl
O
Catalyst
Catalyst Yield (%)
O
(
10 mol%)
H
17
DABCO
86
31
23
OMe
(3.0 equiv)
Scheme 1. Comparison between 21, 22 and DABCO.
2
1
2
rt, neat
20 h
2
(
1.0 equiv)
3-heteroatomsubstituted analogues, which are ofreduced
basicity/nucleophilicity and give lower reaction rates.
Sousa, M. A.; Vasconcellos, M. L. A. A. Synth. Commun.
003, 33, 1383; (i) Aggarwal, V. K.; Emme, I.; Fulford, S.
Y. J. Org. Chem. 2003, 68, 692.
26
2
4
. (a) Roth, F.; Gygax, P.; Frater, G. Tetrahedron Lett. 1992,
3, 1045; (b) Li, W.; Zhang, Z.; Xiao, D.; Zhang, X. J.
Org. Chem. 2000, 65, 3489; (c) Wang, L.-C.; Luis, A. L.;
Agapiou, K.; Jang, H.-Y.; Krische, M. J. J. Am. Chem.
Soc. 2002, 124, 2402; (d) Frank, S. A.; Mergott, D. J.;
Roush, W. R. J. Am. Chem. Soc. 2002, 124, 2404.
In summary, it has been demonstrated for the first time
that bis-aryl ureas such as 4 can serve as efficient, stable
and recyclable DABCO-compatible organocatalysts for
the Baylis–Hillman reaction involving both activated
and challenging substrates, and in this capacity are
considerably more powerful mole per mole promoters of
the reaction than either methanol or water. Preliminary
results implicate a mechanism involving binding to a
3
5. (a) Aug ꢀe , J.; Lubin, N.; Lubineau, A. Tetrahedron Lett.
1994, 35, 7947; (b) Yu, C.; Liu, B.; Hu, L. J. Org. Chem.
2001, 66, 5413; (c) Cai, J.; Zhou, Z.; Zhao, G.; Tang, C.
Org. Lett. 2002, 4, 4723.
Zwitterionic intermediate/transition state,
a
more
6
7
8
. For a systematic study, see: Aggarwal, V. K.; Dean, D. K.;
Mereu, A.; Williams, A. J. Org. Chem. 2002, 67, 510.
. Kawamura, M.; Kobayashi, S. Tetrahedron Lett. 1999, 40,
definitive understanding of which is necessary before
further catalyst optimisation/derivatisation and appli-
cation in areas such as bifunctional catalysis and
asymmetric catalysis can proceed. These studies are now
underway in our laboratory.
1
539.
. Initial claims concerning ionic liquids have been refuted:
a) Rosa, J. N.; Afonso, C. A. M.; Santos, A. G.
(
Tetrahedron 2001, 57, 4189; (b) Aggarwal, V. K.; Emme,
I.; Mereu, A. Chem. Commun. 2002, 1612.
9. (a) Li, G.; Wei, H. X.; Gao, J.; Caputo, T. D. Tetrahedron
Lett. 2000, 41, 1; (b) Basavaiah, D.; Sreenivasulu, B.;
Reddy, R. M.; Muthukumaran, K. Synth. Commun. 2001,
Supplementary material: Experimental procedures,
characterisation data for catalysts 4, 21 and 22, rate
1
13
plots (Table 1), H and C NMR spectra for products
1–18 (Table 1).
1
31, 2987; (c) Basavaiah, D.; Sreenivasulu, B.; Rao, A. J.
J. Org. Chem. 2003, 68, 5983.
1
0. (a) Aggarwal, V. K.; Tarver, G. J.; McCague, R. Chem.
Commun. 1996, 2713; (b) Aggarwal, V. K.; Mereu, A.;
Tarver, G. J.; McCague, R. J. Org. Chem. 1998, 63,
Acknowledgements
7
183; (c) Shi, M.; Jiang, J.-K.; Cui, S.-K. Molecules 2001,
6, 852.
11. (a) Hill, J. S.; Issacs, N. S. J. Phys. Org. Chem. 1990, 3,
Financial support fromTrinity College Dublin is
gratefully acknowledged. We thank Prof. J. Corish for
useful discussions.
2
85; (b) Bode, M. L.; Kaye, P. T. Tetrahedron Lett. 1991,
2, 5611.
3
1
1
2. Resulting in minimal entropy loss on binding with the
target substrate/intermediate.
3. (a) Curran, D. P.; Kuo, L. H. J. Org. Chem. 1994, 59,
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