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.

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