Subscribe to RSS
DOI: 10.1055/s-2007-968576
Zwitterion-Induced Synthesis of Pyrazines and Pyrazolopyridazines
V. Nair*, S. Mathew, A. Biju, E. Suresh
Regional Research Laboratory, Trivandrum and Central salt and Marine Chemicals Research Institute, Bhavnagar, India
Publication History
Publication Date:
22 May 2007 (online)
![](https://www.thieme-connect.de/media/synfacts/200706/lookinside/thumbnails/10.1055-s-2007-968576-1.jpg)
Significance
A synthesis of pyrazoline and pyrazolopyridazine derivatives from the reaction of chalcones with azo diesters is reported. The reaction proceeds via the Huisgen zwitterions, formed from the combination of triphenylphosphine with dialkyl azodicarboxylate, which is suggested to undergo reaction with chalcones or dienones via an oxadiazoline intermediate, which upon fragmentation, followed by ring closure, leads to the product pyrazolines. Vinyl pyrazolines, derived from dienones undergo further reaction with a second dialkyl azodicarboxylate in a Diels-Alder fashion to afford pyrazolopyridazines in good yields. In cases of nonidentical R1 and R2 substituents, the regioselectivity depends on their relative electronegativities. Broad scope for both pyrazoline and pyrazolopyridazine products with respect to aryl substitution was established.