M. Aly, M. Younes, A. Atta
1997
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0
Influential Citations
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Journal
Heterocyclic Communications
Abstract
Pyrazole blue 1 readily reacts with primary aromatic amines to give the corresponding adducts 2a-c,with Ν,Ν-disubstituted aromatic amines yielding 2d-e, with dimethyl amine gives 3 and with benzyl amine to afford rubazonic acid 4. α-Amino acids and thioglycolic acid readily reduces 1 to give 2i. It behaves as a diene to give 6 and as a dienophile yielding 8a,b and lOa-c in DielsAlder cycloaddition. Westoo and others" reported that 1 reacts smoothly with active methylenes and Grignard reagents through a 1,4-addition process across one of the carbonyl groups. Pyrazole blue 1 was prepared according to our modified procedure. The aim of our work was to study the scope and limitation of the reactions of 1 with other reagents such as amines, phenols, thiophenols, water, amino acids and thioglycolic acid. Thus, boiling an equimolar mixture of primary aromatic amines and 1 in dry benzene gave the corresponding adducts 2a-c in moderate to excellent yields (50-96%). However, 1 reacted with 10 fold excess of Ν,Νdisubstituted aromatic amines in ethanol at room temperature to afford 2d ,e in a fairly good yield (56%) together with unidentified decomposition products. The structures of 2a-e was assigned on the basis of spectral and analytical data. It is believed that compounds 2a-e are obtained via a 1,4-addition process across one of the carbonyl groups. On the other hand, stirring of 1 with 10 fold excess of dimethyl amine in absolute ethanol for 5 days at ambient temperature gave 77% yield of 3. The structure of 3 was established on the basis of its spectral and analytical data. There is further supporting evidence, thus 3 was authentically prepared by the reaction of the diketone 5 and dimethyl amine. Interestingly, stirring a mixture of 1 (1 mmol) and benzyl amine (10 mmol) in ethanol at room temperature for 30 minutes afforded rubazonic acid 4 8 in a good yield (72%). We believe that the diketone 5 is obtained in situ as an intermediate (Scheme), which in turn reacts with benzyl amine to give 4. We reported recently that 5 reacts readily with α-amino acids and amines to give 4 . Similarly, 1 reacted with phenol and thiophenol yielding 2f and 2g in 48% and 51% yields respectively. However, boiling 1 with aqueous ethanol gave 2h in a 77% yield. Surprisingly, boiling an equimolar mixture of 1 and α-amino acid, e.g., glycine, alanine, serine, valine, threonine and phenylglycine in glacial acetic acid for 1 hour gave 2i in 72%, 68%, 65%, 61%, 63% and 69% yields respectively. On the other hand, refluxing 1 with 2 fold excess of thioglycolic acid in dry benzene for 5 hours yielded 52% of 2i. The structure of 2i was established on the basis of its spectral and analytical data. It was also confirmed by the preparation of an authentic sample of 2i via a different route. It also attracted our attention to study the reactivity of 1 in both normal and inverse electron demand DielsAlder cycloaddition reactions. Thus heating under reflux pyrazole blue 1 with an excess of ethyl vinyl ether for 0.5h afforded a reasnable good yield (67%) of the corresponding cycloadduct 6. The sructure of 6 was established on the basis of its spectral and analytical data. In contrast, compound 1 reacted with homoand heterodienes as a dieneophile.Thus, boiling an equimolar mixture of 1 and dienes 7a,b in acetonitrile for 0.5h gave 8a,b in 58 and 66% yields respectively. Analogously, 1 reacted with 231 Vol. 3, No. 3, 1997 Addition And Cycloaddition Reactions With Pyrazole Blue Mev Me Ί ι ι — ι i % A C A N ' N Ph Ph Me OH Y N. -NMe-> Τ Ph 3 Me Y N. Ν I Ph -N. Me f r ί N' Ph Me R Η Y 1 Me Ν ^ ^ s N O O N Ph 2 Ph a, R = C6H5NH " b, R = ρ MeC6H4NH c, R = ρ MeOC6H4NH d, R = ρ Me2NC6H4NH e, R = ρ Et2NC6H4NH f, R = C6H50 g, R = C6H5S i, R = H Me Ν Ph 5 h, R = ο ζ ? Ph Me Ph \ ν t> Me ° S / H b ΙΪ Hb V OC2H5 Ph 6 Me. R 2 a , R = H b, R = Me % > o o V N Ph 8 Ph Ph λ .Η Ν-Ar Me ^ Ν o O N Η Ν—Ar ι ι Ph Ph ? a , Ar = C6HS 10 a, Ar = C6HS b, Ar = ρ MeOC6H4 b, Ar = ρ MeOC6H4 c, Ar = /> MeC6H5 c, Ar= ρ MeC6H4