Preparation of novel tricyclic ring systems containing the pyridazinone ring

Abstract

Novel tricyclic ring systems, irmdazo[3,4‐d]pyridazino[4,5‐b][1,4]thiazines 3, imidazo[2,1‐b]pyridazino[4,5‐e][1,3,4]thiadiazines 15 and 18 were prepared by the reaction of 5‐amino‐4‐chloropyridazin‐3(2H)‐ones 1 and 5(4)‐(1‐methylhydrazino)‐4(5)‐chloropyridazin‐3(2H)‐ones 13 (16) with isothiocyanates 2 and 7.

Benzofuranyl‐pyran‐2‐ones, ‐pyridazines, and ‐pyridones from naturally occurring furochromones (visnagin and khellin)

“…Pyridazines comprise a very interesting class of heteroaromatics because of their significant biological activities [9][10][11][12]. So, enaminones 2a,b coupled with 4-nitrophenyldiazonium salt in the presence of sodium hydroxide to yield 3-(benzofuran-5-yl)-2-[(4-nitrophenyl)-hydrazono]-3-oxo-propanals 8a,b which are excellent precursors for the synthesis of pyridazine derivatives.…”

“…In particular, derivatives of this system represent a new class of HIV protease inhibitors [7,8]. Significant biological activities are also associated with substituted pyridazines [9][10][11][12], pyridones [13], pyrazoles [14,15], and isoxazoles [16,17]. In view of these facts and in continuation of our work on the synthesis of heterocyclic compounds derived from the naturally occurring furochromones (visnagin and khellin) of pharmacological interest [18,19], it was worthwhile to synthesize new benzofuran derivatives by incorporating these biogenic moieties.…”

Synthesis of 1,3,4-Thiadiazines and 1,3,4-Oxadiazines

“…The reaction of 6-chloroquinoline-5,8-dione hydrochloride (12) with thiosemicarbazide or semicarbazide gave 2-amino-4H-1,3,4-thiadiazino[6,5-s]quinoline-5,lO-dione (13) or 2amino-4H-l,3,4-oxadiazino[6,5-~quinoline-5,1O-dione (14), respectively (Scheme 6).8 The reaction of 2,3-dichloronaphthoquinone (15) (27), which was cyclized into the imidazo (31), while the reaction of compound (30) with benzyl isothiocyanate afforded the adduct (32), whose reaction with sodium hydroxide …”

An Efficient Route to Pyridazino[4, 3‐e][1, 3, 4]thiadiazines

“…These compounds have been described as being potential inhibitors of cyclic nucleotide phosphodiesterase , dyestuff , and precursors of herbicides . Despite their importance from pharmacological and synthetic point of views, comparatively few methods for their preparation have been reported , and among those structural isomer, pyridazino[4,3‐ e ][1,3,4]thiadiazine ( 3 ) has been largely overlooked. The only undisputed example of this heterocyclic compound has been synthesized in two steps by Oda and his co‐workers through cyclocondensation of 6‐chloro‐2‐methyl‐5‐(1‐methylhydrazino)‐3(2 H )‐pyridazinone with benzyl isothiocyanate in the presence of sodium hydroxide .…”