Synthesis of Pyridazine Derivatives with Sulfur-Containing Substituent. IV. The Concurrent Formation of Dipyridazo [3, 4-b : 3', 4'-e]-1, 4-dithiin and Dipyridazo [3, 4-b : 4', 3'-e]-1, 4-dithiin Derivatives by Starting with 3-Chloro-4-mercapto-5-substituted Pyridazines. (3)

抄録

3-Chloro-4-mercapto-5-ethoxypyridazine (1) was heated under reflux in abs. ethanol for three hours to form concurrently four products with novel rings in the dipyridazo-1, 4-dithiin system, 4, 9-diethoxydipyridazo [3, 4-b : 3', 4'-e]-1, 4-dithiin (pale yellow needles, mp 211°, 13% in yield) (Ia), 4, 6-diethoxydipyridazo [3, 4-b : 4', 3'-e]-1, 4-dithiin (colorless needles, mp 260°, 12% in yield) (IIa), dipyridazo [3, 4-b : 3', 4'-e]-1, 4-dithiin-4, 9 (1H, 6H)-dione (colorless solid, mp>300°, 24% in yield) (Ib), and dipyridazo [3, 4-b : 4', 3'-e]-1, 4-dithiin-4, 6 (1H, 9H)-dione (colorless solid, mp>300°, 16% in yield) (IIb). Structural assignment of the compounds, Ia, IIa, Ib and IIb, was confirmed by their physico-chemical constants and chemical experimental evidences. Similar concurrent formations of an isomeric pair of 4, 9-disubstituted dipyridazo-[3, 4-b : 3', 4'-e]-1, 4-dithiins (I series isomers) and 4, 6-disubstituted dipyridazo [3, 4-b : 4', 3'-e]-1, 4-dithiins (II series ones) were also observed in those cases in which heating 3, 5-dichloro-4-mercaptopyridazine (3), 3-chloro-4-mercapto-5-benzylthiopyridazine (4) and 3-chloro-4-mercapto-5-morpholinopyridazine (5) in similar reaction conditions (heating in proper polar solvents for proportionatd periods) formed a pair of the 4, 9-dichloro- (colorless needles, mp 275°, only trace in yield) (Ic) and 4, 6-dichloro derivative (pale yellow needles, mp 307°(decomp.), only trace in yield) (IIc), 4, 9-dibenzylthio- (yellow crystals, mp 230°, 29% in yield) (Id) and 4, 6-dibenzyl derivative (red crystals, mp 252°, 23% in yield) (IId), and 4, 9-dimorpholino- (colorless crystals, mp 268°, 38% in yield) (Ie) and 4, 6-dimorpholino derivative (colorless needles, mp 291°, 25% in yield) (IIe), respectively. A rather complex cyclization furnishing the concurrent formation of two pairs of the dipyridazo-1, 4-dithiin derivatives was found in the reaction of heating 3-chloro-4, 5-dimercaptopyridazine (6) in a similar reaction condition, followed by benzylation, in which a pair of the derivatives with another novel ring, dipyridazo [3, 4-b : 4', 5'-e]-1, 4-dithiin, the 4, 9-dibenzylthio- (colorless plates, mp 168°, 5% in yield) (VI) and 4, 6-di-benzylthio derivative (yellow needles, mp 210°, 11% in yield) (VII) and another pair of derivatives with a known ring, dipyridazo [4, 5-b : 4', 5'-e]-1, 4-dithiin, the 1, 6-dibenzylthio-(yellow needles, mp 178°, 19% in yield) (IV) and the 1, 9-dibenzylthio derivative (colorless needles, mp 170°, 9% in yield) (V) and none of Id and IId or 1, 6-dichlorodipyridazo-[4, 5-b : 4', 5'-e]-1, 4-dithiin (If) and 1, 9-dichloro derivative (IIf) was detected. NMR spectra of some dibenzylthiodipyridazo-1, 4-dithiin derivatives were compared. A discussion of the cyclization mechanism involved in these reactions is also proposed.