Pyridazines, 1,2,3,6-tetrahydro— from

Hydrogen peroxide cupric chloride Partial dehydrogenation of N-heteroeyclics 1,2,3,4-Tetrahydro- from hexahydro-pyridazines... 

Dihydropyridazines have not been prepared by direct cycliza-tions reductions of pyridazines and oxidations of reduced pyridazines are known. 3,6-Diphenylp3n idazine is reduced with sodium and ethanol to the 1,2-dihydro derivative and the 1,2-dicarbethoxy analog is formed in a selenium dioxide oxidation of the corresponding 1,2,3,6-tetrahydro compound. 1-Carbethoxy- or 1,2-dicarbethoxy-1,2-dihydropyridazine was obtained similarly from an alkali treatment of 1,2-dicarbethoxyhexahydropyridazine. l,2-Dihydro-3,6-diphenylpyridazine is unstable and oxidizes to the parent pyridazine in the presence of air or on attempted acetylation. ... 

Pseudothiohydantoine, as acyclic intermediate, in reaction of o-halogeno acids or esters with thiourea, 232. See also 2-Amino-4-hydroxythiazole Pyridazines (4,7-dioxo-4,5,6,7-tetrahydro-thiazolo[4,5d]), preparation of, 206 Pyridine, electronic structure, 36, 39, 46 ultraviolet absorption, 47 thiazolylation of, 373 2-(4-Pyridyl)-4-carboxyethylthiazoie, from thioisonicotinamide and ethyl bromopyruvate, 198... 

A new route to pyridazine analogues of dihydropyridine calcium antagonists has been devised. Ethyl l,3-dithiolane-2-carboxylate was found to add efficiently, as its lithium salt, to benzylidene derivatives prepared from aryl aldehydes and diethylmalonate or ethyl acetoacetate the dithiolane adducts were readily deprotected using NBS (Scheme 98). The resultant diketo derivatives (121) were cyclized with hydrazine to give either 1,4-dihydropyridazines (122) or l,4,5,6-tetrahydro-6-... 

An ethanolic soln. of 2,3-dibenzoyl-2,3-dihydro-5-phenylfuran and 95%-hydrazine refluxed 2 hrs. l,2,4a,8a-tetrahydro-3,5,8-triphenylpyridazino[4,5-c]pyridazine. Y 50%. F. e., also fused heterocyclics from functionalized 1,3-dipoles, s. B. E. Landberg and J. W, Lown, Soc. Perkin I 7975, 1326. 

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