A facile and general transition‐metal‐free access to 1‐substituted‐4‐quinazolinones 2 has been achieved based on the proline‐mediated cyclization of carbamoylbenzamides 1 in the presence of potassium t‐butoxides in DMSO at 100 °C within several hours. The gram‐scale synthesis of 1‐phenyl‐4‐quinazolinone 2 a has also been achieved without the loss of efficiency. The one‐pot synthesis of 1‐phenyl‐4‐quinazolinone 2 a has proven to be possible starting from 2‐bromobenzamide and phenylisocyanate in an acceptable yield. The present reactions were assumed to proceed through radical intermediates as the major path and also the SNAr route as a minor path based on several control experiments.

A series of biologically important 3-substituted-2-thixo-4quinazolinones have been synthesized starting from methyl 2isothicyanatobenzoate and amines without the use of additives under mild reaction conditions in water. This transformation tolerates a wide range of amines, which include anilines, alkyl amines, and hydrazines, to afford 60 diverse 3-substituted-2-thixo-4-quinazolinones including 34 new compounds at 60 °C for 30 min in good yields. This method avoids the use of organic solvent and the generation of toxic waste to demonstrate a cost efficient, green and sustainable method for the synthesis of 2-thixo-4-quinazolinone derivatives as valuable heterocycles for biological and materials studies.

A facile and environmentally benign access to N-aryl/alkyl-4H-benzoxazin-2-amines is achieved from 1-[2-(hydroxymethyl)phenyl/alkyl]-3-phenylthioureas under transition-metal-free conditions. The conversions occur smoothly in the presence of a catalytic amount of molecular iodine and hydrogen peroxide as the oxidant in tetrahydrofuran at room temperature to afford moderate to good yields (28–90%) of the desired products within 2 hours. This method reports the first examples of the catalytic transformations of 1-[2-(hydroxymethyl)phenyl/alkyl]-3-phenylthioureas into N-aryl/alkyl-4H-benzoxazin-2-amines based on desulfurative cyclization.