title: Diazo Strategy for the Synthesis of Pyridazines: Pivotal Impact of the Configuration of the Diazo Precursor on the Process.
abstract: Phosphazenes of vinyldiazocarbonyl compounds having cis stereochemistry of the functional groups on the vinyl bond readily produce pyridazines by a diaza-Wittig process, whereas their counterparts with trans configuration remain intact under similar reaction conditions. Upon UV irradiation trans-phosphazenes furnish pyridazines through a tandem trans-to-cis isomerization followed by intramolecular cyclization. At elevated temperatures trans-(triphenyl)phosphazenes dissociate to give the initial vinyldiazo compounds, which produce pyrazoles in high yields. The first theoretical study on the mechanism of the diaza-Wittig process by DFT calculations at the M06-2X/6-31G(d) level of theory suggest that for the cis-phosphazenes a rapid tandem [2+2] cycloaddition/cycloelimination process with low energy barriers is preferred over trans isomers.
authors.affiliation: Department of Organic Chemistry, St-Petersburg State University, University pr. 26, 198504, Saint-Petersburg (Russia). vnikola@VN6646.spb.edu.
authors.forename: Valerij A
authors.initials: VA
authors.lastname: Nikolaev
authors.affiliation: Institute of Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz (Austria). david.cantillo@uni-graz.at.
authors.forename: David
authors.initials: D
authors.lastname: Cantillo
authors.affiliation: Institute of Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz (Austria).
authors.forename: C Oliver
authors.initials: CO
authors.lastname: Kappe
authors.affiliation: Department of Organic Chemistry, St-Petersburg State University, University pr. 26, 198504, Saint-Petersburg (Russia).
authors.forename: Jury J
authors.initials: JJ
authors.lastname: Medvedev
authors.affiliation: University of Southern California, 837 Bloom Walk, Los Angeles, CA 90089-1661 (USA). gprakash@usc.edu.
authors.forename: G K Surya
authors.initials: GK
authors.lastname: Prakash
authors.affiliation: Department of Organic Chemistry, St-Petersburg State University, University pr. 26, 198504, Saint-Petersburg (Russia).
authors.forename: Murat B
authors.initials: MB
authors.lastname: Supurgibekov
keywords: Wittig reactions; cyclization; isomerization; phosphazenes; photochemistry