Abstract
3-Oxo-3-phenyl-2-(p-tolylhydrazono)propanal (1a) undergoes condensation with ethyl cyanoacetate in acetic acid in the presence of ammonium acetate to yield either 2-hydroxy-6-phenyl-5-p-tolylazonicotinic acid ethyl ester (6a) or 2-amino-6-phenyl-5-p-tolyl-azonicotinic acid ethyl ester (8), depending on the reaction conditions. Similarly, other 3-oxo-3-aryl-2-arylhydrazonopropanals 1a,b condense with active methylene nitriles 2c,d to yield arylazonicotinates 6b,c. In contrast, 2-[(4-nitrophenyl)-hydrazono]-3-oxo-3-phenyl-propanal (1c) reacts with ethyl cyanoacetate to yield ethyl 6-(4-nitrophenyl)-2-oxo-2,6-dihydropyrido[3,2–c]cinnoline-3-carboxylate (11), via a novel 6π-electrocyclization pathway. Finally, 3-oxo-2-(phenylhydrazono)-3-p-tolylpropanal (1d) condenses with 2a–c to yield pyridazinones 13a–c.
Highlights
The chemistry of arylhydrazonopropanals 1 has attracted considerable attention [1,2]
Because arylazonicotinates are a valuable class of arylazopyridine dyes whose chemistry has attracted some interest as new disperse dyes [10,11], it seemed of value to undertake an investigation aimed at exploring the potential utility of arylhydrazonopropanals as precursors for the preparation of these targets
In the first phase of the current effort, we observed that reaction of the 3-oxo-3-phenyl-2-(ptolylhydrazono)propanal (1a) with ethyl cyanoacetate in acetic acid for 30 min in the presence of a catalytic amount of ammonium acetate leads to formation of the ethyl 2-hydroxy-6-phenyl-5-ptolylazonicotinate (6a; Scheme 1) whose structure was established by X-ray crystallographic analysis (Figure 1) [12]
Summary
The chemistry of arylhydrazonopropanals 1 has attracted considerable attention [1,2]. These substances have proven to be valuable precursors of 3-aroylpyrzoles [3], 3-aroylpyridazine-4,6dicaboxylic acids [4], 3-aroylcinnolines [5], as well as novel 3-aroyl-1,6-dihydropyridazines [6]. Because arylazonicotinates are a valuable class of arylazopyridine dyes whose chemistry has attracted some interest as new disperse dyes [10,11], it seemed of value to undertake an investigation aimed at exploring the potential utility of arylhydrazonopropanals as precursors for the preparation of these targets. A recent investigation, described below, has led to the synthesis of two different types of substances, including 2-hydroxyarylazonicotinic acid ethyl esters and 2-aminoarylazonicotinic acid ethyl esters, along with ethyl 6-(4-nitrophenyl)-2-oxo-2,6-dihydropyrido[3,2–c]cinnoline-3carboxylate, which forms via a pathway involving a novel 6 -electrocyclization reaction
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