139185-18-5Relevant articles and documents
Diversity of Reaction of Azoalkenes in Cycloadditions
Ferguson, George,Lough, Alan J.,Mackay, Donald,Weeratunga, Gamini
, p. 3361 - 3370 (2007/10/02)
Reactions of the azoalkenes (E,E)-4-methyl-N-phenyl-2,3-diazapenta-2,4-diene-5-carboxamide 2 and methyl (E,Z)-3-methyl-4-phenylcarbamoyl-1,2-diazabuta-1,3-diene-1-carboxylate 3, having respectively an electron-rich and an electron-poor group on nitrogen, are described.Compound 2, is a stable compound and its stereochemistry was established as E,E by X-ray crystallography; compound 3 is much less stable and was assigned the E,Z stereochemistry on the basis of its 1H NMR spectrum and the crystal structure of a derivative 17.Of a wide variety of substrates, only azo esters react with 2, which behaves as a heterodiene.The 1,2,3,6-tetrahydro-1,2,3,4-tetrazine 7 obtained from 2 by reaction with dimethyl azodicarboxylate is unstable and on work up yields a 4,5-dihydro-1H-1,2,3-triazole 9a (whose structure was established by X-ray crystallography).This isomerisation is probably acid catalysed since, by inclusion of acid, 7 tautomerises to a 1,2,3,4-tetrahydro-1,2,3,4-tetrazine 8 which then ring contracts to 9a, followed by a decarboxylative elimination of methyl carbamate to yield the 1,2,3-triazole 10.The azoalkene 3 is unreactive to electron-poor substrates, but reacts with cyclopentadiene both as a heterodiene and as a dienophile (at C=C) to give as Diels-Alder adducts the tetrahydro-1H-cyclopentapyridazine 16 and the bicyclohept-2-ene 17 respectively.With ethyl vinyl ether 3 gave the ethoxytetrahydropyridazine 18 which eliminated EtOH in acid to the dihydro tautomers 19 and 20 which on basic hydrolysis and oxidation give the pyridazine 21.
