4196
J. Chen et al.
8. (a) Hantzsch, A. Stereochemical arrangement of atoms in molecules
containing nitrogen. Ber. Dtsch. Chem. Ges. 1890, 23, 1474; (b) Fabiano,
E.; Golding, B. T. On the mechanism of pyrrole formation in the knorr pyr-
role synthesis and by porphobilinogen synthase. J. Chem. Soc., Perkin Trans.
1 1991, 3371; (c) Ferreira, V. F.; De Souza, M. C. B. V.; Cunha, A. C.;
Pereira, L. O. R.; Ferreira, M. L. G. Recent advances in the synthesis of pyr-
roles. Org. Prep. Proced. Int. 2002, 33, 411; (d) Kleinspehn, G. G. A novel
route to certain 2-pyrrolecarboxylic esters and nitriles. J. Am. Chem. Soc.
1955, 77, 1546; (e) Hamby, J. M.; Hodges, J. C. a-Amino ketones from amino
acids as precursors for the knorr pyrrole synthesis. Heterocycles 1993, 35,
843; (f) Alberola, A.; Ortega, A. G.; Sadaba, M. L.; Sanudo, C. Versatility
of Weinreb amides in the knorr pyrrole synthesis. Tetrahedron 1999, 55,
6555; (g) Elghamry, I. Synth. Commun. 2002, 32, 897.
9. (a) Yadav, J. S.; Reddy, B. V. S.; Eeshwaraiah, B.; Gupta, M. K.
Bi(OTf)3=[bmim]BF4 as novel and reusable catalytic system for the synthesis
of furan, pyrrole, and thiophene derivatives. Tetrahedron Lett. 2004, 45, 5873;
(b) Braun, R. U.; Zeitler, K.; Mueller, T. J. J. A novel one-pot pyrrole synth-
esis via a coupling–isomerization–Stetter=Paal–Knorr sequence. Org. Lett.
2001, 3, 3297; (c) Curini, M.; Montanari, F.; Rosati, O.; Lioy, E.; Margarita,
R. Layered zirconium phosphate and phosphonate as heterogeneous catalyst
in the preparation of pyrroles. Tetrahedron Lett. 2003, 44, 3923; (d) Banik, B.
K.; Samajdar, S.; Banik, I. Simple synthesis of substituted pyrroles. J. Org.
Chem. 2004, 69, 213; (e) Balme, G. Heterocycle synthesis: Pyrrole syntheses
by multicomponent coupling reactions. Angew. Chem., Int. Ed. 2004, 43,
6238; (f) Bharadwaj, A. R.; Scheidt, K. A. Catalytic multicomponent synth-
esis of highly substituted pyrroles utilizing a one-pot Sila–Stetter=Paal–Knorr
strategy. Org. Lett. 2004, 6, 2465; (g) Ballini, R.; Barboni, L.; Bosica, G.;
Petrini, M. 2,5-Dialkylfurans and nitro alkanes as source of 2,3,5-trialkylpyr-
roles. Synlett 2000, 391; (h) Raghavan, S.; Anuradha, K. Solid-phase synth-
esis of heterocycles from 1,4-diketone synthons. Synlett 2003, 711; (i)
Quiclet-Sire, B.; Quintero, L.; Sanchez-Jimenez, G.; Zard, Z. A practical var-
iation on the Paal–Knorr pyrrole synthesis. Synlett 2003, 75; (j) Wang, B.;
Gu, Y. L.; Luo, C.;Yang, T.; Yang, L. M.; Suo, J. S. Pyrrole synthesis in ionic
liquids by Paal–Knorr condensation under mild conditions. Tetrahedron Lett.
2004, 45, 3417; (k) Wang, B.; Kang, Y. R.; Yang, T.; Yang, L. M. Fe3þ-Mon-
tmorillonite as effective, recyclable catalyst for Paal–Knorr pyrrole synthesis
under mild conditions. Synth. Commun. 2005, 35, 1051.
10. (a) Ruault, P.; Pilard, J. F.; Touaux, B.; Boullet, F. T.; Hamelin, J. Rapid
generation of amines by microwave irradiation of ureas dispersed on clay.
Synlett 1994, 935; (b) Danks, T. N. Microwave assisted synthesis of pyrroles.
Tetrahedron Lett. 1999, 40, 3957; (c) Minetto, G.; Raveglia, L. F.; Sega, A.;
Taddei, M. Microwave-assisted Paal–Knorr reaction—Three-step regiocon-
trolled synthesis of polysubstituted furans, pyrroles, and thiophenes. Eur. J.
Org. Chem. 2005, 5277; (d) Minetto, G.; Raveglia, L. F.; Taddei, M.
Microwave-assisted Paal–Knorr reaction: A rapid approach to substituted
pyrroles and furans. Org. Lett. 2004, 3, 389.