A simple and efficient one‐pot synthesis of 5‐alkylidene‐3‐pyrrolin‐2‐ones 3a,e‐g from N‐acylaminoketones is described. A mechanism is proposed and it is substantiated by synthethising and converting the proposed intermediates into the pyrrolinones 3a,e‐g.
Reactions of the iminoesters 3a‐c with hydrazine or 1,2‐dimethylhydrazine gave 4,5‐dihydro‐4a‐c or 2,5‐dihydro‐1,2,4‐triazin‐6(1H) ones 7a‐c, respectively. When methylhydrazine was employed, 1‐methyl‐4, 5‐dihydro‐ 5a‐c and 2‐methyl‐2,5‐dihydro‐1,2,4‐triazin‐6(1H) ones 6a‐c were obtained. Compounds 6a‐c exist as zwitterions in the solid state and in polar aprotic solvents.
Depending on the substitution on the hydrazine moiety, thermolysis of 3-phenyl-l,2,4-oxadiazol-5-ylhydrazines(1)-(5) gives variable amounts of 1 -amino-A2-1,2,4-triazolin-5-ones (1 3) or (1 7), AZor A3-1,2,4-triazolin-5ones (1 2), (1 8), or (1 9), and the s-triazine (20). A possible mechanism accounting for the products and the effects is discussed. A diradical intermediate and a hydrogen transfer from the reaction medium are suggested on the basis of the effect of benzoyl peroxide on the reaction and on the behaviour of the hydrazines (1)-(4) towards catalytic h yd rog en at i on.
The synthesis and properties of 4,6‐dichloro‐ (IV), 4‐chloro‐ (XII) and 6‐chloro‐3‐methyl‐isoxazolo[5,4‐b]pyridine (XI) are described. Depending on the reaction conditions compound IV with hydrazine or methoxide gave mono‐ or bi‐substituted products. The halogen atom at the 4‐position was shown to be the more mobile.
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