The Chemistry of Cinnolines.

Methods for the synthesis of cinnolines (review)

“…In spite of its long history the Richter reaction has only attracted the attention of investigators in the last decade as a method for the synthesis of 4-halocinnolines. At the same time the Widman-Stoermer and Borsche-Herbert reactions are already well-studied reactions and are discussed in detail in the reviews [25][26][27][28][29][30].…”

“…The cinnolines are not formed in the presence of strong accepting substituents (R 1 = COOH). In some cases the presence of a phenyl substituent at the β-carbon atom of the double bond leads to the formation of phenanthrene, taking place by the Pschorr reaction, in competition with the cyclization [25][26][27][28][29][30]. The Widman-Stoermer reaction is rarely used these days since the obtained 4-alkyl-and aryl(hetaryl)-substituted cinnolines only find limited use in contemporary synthesis.…”

“…The method involves diazotization of ortho-aminoacetophenones followed by cyclization of the obtained arenediazonium salt (Scheme 17) [25][26][27][28][29][30].…”

“…In contrast to the Widman-Stoermer reaction, in the presence of a phenyl substituent in the acetyl fragment of the initial compound the formation of 9-phenanthrol by the Pschorr reaction can be avoided, and in this case 4-hydroxycinnoline is the only product [60]. The limited application of this method is due to the difficulties involved in the synthesis of the initial substituted ortho-aminoacetophenones and to the side reactions involving substitution in the benzene ring [25][26][27][28][29][30].…”

Unusual Reactions Between Aromatic Carbon Supernucleophiles and 1,2‐Diazabuta‐1,3‐dienes: Useful Routes to New Pyrazolone and Cinnoline Derivatives

“…[10] Some derivatives exhibit anti-inflammatory and antibiotic activity. Sometimes they are synthesized from o-aminophenylethylene or o-aminoacetophenones, [11] but the main routes are the cyclization of ortho-substituted arylhydrazones or the diazotization of o-substituted anilines. [12][13][14] The cyclization of hydrazones is achieved through Friedel-Crafts-type reactions.…”