Studies on the Reactions of Heterocyclic Compounds. V. Syntheses of Diazinium Ylides and Their Conversion to Azaindolizines

Pyrrolo[1,2-b]pyridazines. A revisit

“…One of the most useful methods for obtaining pyrrolopyridazine derivatives is the 1,3-dipolar cycloaddition between pyridazinium N-ylides and activated olefinic or acetylenic dipolarophiles. The synthesis of pyrrolo[1,2-b]pyridazines through 1,3-dipolar cycloadditions has been described in over 35 papers, using acetylenic, [68][69][70][71][72][73][74][75][76][77][78][79][80] olefinic, [80][81][82][83][84][85][86][87][88][89][90][91][92] as well as both acetylenic and olefinic dipolarophiles. [93][94][95][96][97][98][99][100][101][102][103] The advantages of the method consist of: a) the availability of the raw material, as pyridazinium salts are easily obtained from pyridazine or its derivatives and halogenated derivatives, and b) the pyridazinium N-ylide generation and the cycloaddition are performed "one-pot", and the cycloaddition does not require special reaction conditions.…”

“…68 Heteroaromatic N-ylides can be classified by the substitution degree at the exocyclic carbanion as unsubtituted, monosubstituted and disubstituted. In [3+2] cycloadditions pyridazinium methanide (R 1 =H) 37, 69 pyridazinium carbanion monosubstituted 38 and carbanion disubstituted 39 N-ylides [70][71][72][73][97][98][99] were used as dipolarophiles (Scheme 21). The yields of the pyrrolopyridazines depend on the following factors: the reactivity and stability of the ylide and the reactivity of the dipolarophile.…”

“…[70][71][72][97][98][99] It must be mentioned that pyridazinium dicyanomethylides 39 are very stable N-ylides, which translates into the ability to react with low reactivity acetylenic dipolarophiles, such as bis(trimethylsilyl) acetylene. The preparation of dicyanomethylides 39a-f was performed using the method described by Linn et al 105 from pyridazines and tetracyanoethylene oxide(Scheme 23).…”

“…In the case of reacting ylids 39a, 39b and 39d with cyanoacetylene, 5,7-dicyano-pyrrollopyridazines substituted in the 5 position with a hydrogen, methoxy and ethoxy group, respectively (Scheme 24). 71 At the same time, another group of researchers 70 …”

2-Substituted-8-methyl-3,6-dihydroimidazo[4,5-c]pyrazolo[3,4-e]pyridazine as an anti-inflammatory agent

“…Various synthetic routes have been followed for synthesizing the fused ring pyrazolo-pyridazine system and their derivatives (Druey, 1958;Caronna et al, 1986;Kobayashi et al, 1971;Kasuga et al, 1974;Shawali, 1977;Kurihara et al, 1980). The synthesis of pyridazines from 1,4-diketones and hydrazine hydrate is one of the best known procedures (Hendrickson et al, 1964).…”