A Microwave Assisted Diazo Coupling Reaction: The Synthesis of Alkylazines and Thienopyridazines

Heating diazoaminobenzene with active methylene compounds 1–3 in microwave oven in acetic acid, in the presence of hydrochloric acid, afforded the corresponding arylhydrazones 5–7. These reaction products were condensed with ethyl cyanoacetate in a domestic microwave oven after 1–2 minutes heating to yield the pyridazinones 8–12. Compounds 8c and 12 reacted with sulfur in basic DMF solution, in microwave oven using MORE technology to yield the thienopyridazinone 14 and 16 respectively. While 17 was produced when 8b was treated like wise with sulfur and DMF in the presence of piperidine. Compounds 16 coupled with aromatic diazonium salts to yield arylazo derivatives 21a–c.     

Exploring the scope of the Gewald reaction: Expansion to a four-component process

An efficient four-component reaction was developed to take advantage of the reactivity of the 2-aminothiophene-3-carbonitrile functionality, which is obtained during the classical three-component Gewald reaction. Various α-methylene bearing ketones were reacted with malononitrile, elemental sulfur, and aryl/heteroarylnitrile derivatives in t-BuOH/NaOH to afford 2-arylthieno[2,3-d]pyrimidin-4-amines in high yields. Preliminary studies revealed the photophysical properties of the products and their potential for use as metal sensors.     

Synthesis and Reactivity of 2-(1,2,3-Dithiazol-5- Ylidene)Aminothiophenes

The reaction of aminothiophenes (1) with Appel's salt (2) affords 2-(1,2,3-dithiazol-5-ylidene)aminothiophenes (3). Under the action of ZnCl₂, the latter compounds are transformed into 1,3-oxazin-4-one systems (4). The reactions of compounds 4 with dienophiles under atmospheric or high pressure give thienopyridines (6–11); the reactions with amines produce pyrimidinones (12) and guanidines (14–15).