Temperature‐Controlled Cyclization of Anthranilic Acids to 2‐Thioxoquinazolin‐4‐One or Thiazoloquinazolinone Derivatives Under Microwave Irradiation

ABSTRACT

Investigation of the microwave‐assisted condensation of anthranilic acid derivatives with ethylpiperidine isothiocyanates into 2‐thioxoquinazolin‐4‐ones revealed an intramolecular cyclization into 2,3‐dihydro‐5 H ‐thiazolo[2,3‐ b ]quinazolinones. The study of reaction parameters demonstrated that temperature is a key factor controlling this transformation, while anthranilic acid substituents further modulate the reaction outcome. Here we report the promotion of the intramolecular cyclization to thiazoloquinazoline at high temperatures (200°C), whereas lower temperature (125°C) selectively favors the formation of 2‐thioxoquinazolin‐4‐one in good yield. These findings provide refined conditions for the synthesis of 2‐thioxoquinazolin‐4‐one derivatives and expand the way to synthesize 2,3‐dihydro‐5 H ‐thiazolo[2,3‐ b ]quinazolinone derivatives of potential medicinal interest.