With more than One N Atom

Five membered ring systems with more than one N atom 

Albany Molecular Research, Inc., Albany, NY USA Larrv.Yet albmolecular.com 

The synthesis and chemistry of pyrazoles, imidazoles, and 1,2,3-triazoles were actively pursued in 2006. A review on the cross-coupling reactions on azoles with two and more heteroatoms for pyrazoles and imidazoles has been published 06EJO3283 . Publications relating to 1,2,4-triazole and tetrazole chemistry were not particularly well represented this year. The solid-phase and combinatorial chemistry of these ring systems have not been investigated compared to past years. No attempt has been made to incorporate all the exciting chemistry or biological applications that have been published this year. 

A short review has been published on the utilization of chiral enaminones and azomethine imines in the synthesis of functionalized pyrazoles 06ARK35 . 

Hydrazones are also useful substrates in the preparation of pyrazoles. Reaction of N-monosubstituted hydrazones with nitroolefins led to a regioselective synthesis of substituted pyrazoles 060L3505 . lf/-3-Ferrocenyl-l-phenylpyrazole-4-carboxaldehyde was achieved by condensation of acetylferrocene with phenylhydrazine followed by intramolecular cyclization of the hydrazone obtained under Vilsmeier-Haack conditions 06SL2581 . A one-pot synthesis of oxime derivatives of l-phenyl-3-arylpyrazole-4-carboxaldehydes has been accomplished by the Vilsmeier-Haack reaction of acetophenone phenylhydrazones 06SC3479 . 

A review has been published on the stereoselective cycloadditions of nitrilimines as a useful tool in the synthesis of a number of enantiopure heterocycles containing the 4,5-dihydropyrazole ring 05H(65)2513 . 

Addition of hydrazines to 1,3-difunctional compounds is one of the most common methods employed for the preparation of pyrazoles. For example, several synthesis of pyrazoles have been reported where azide reagents are added to a,P-unsaturated systems. Reactions of trifluoroacetyl enol ether (thiophene) 1 with hydrazines afforded 3-(2-furyl) or 3-(2-thienyl)pyrazoles 2 05S2744 . A regiospecific one-pot synthesis of trifluoromethyl-substituted heteroaryl pyrazolyl ketones has also been disclosed 05JHC631, 05JHC1055 . 1,3,5- 

---

Furan and its benzo derivatives 97PF1C117, 98PF1C129, 99PF1C144. Thiophenes, selenophenes, andtellurophenes 97PF1C77,98PF1C87,99PF1C102. Five-membered heterocycles with more than one N atom 97PF1C148,... 

Five-Membered Ring Systems With More than One N Atom... 

---