Cross-dehydrogenative coupling reactions have been utilized to alkylate 4(3H)-quinazolinones with ethers and amides, using catalytic n-Bu₄NI and t-BuOOH as oxidants. The reactions with amides represent the first examples under such conditions. Studies via inter- and intramolecular competitive experiments with protio and deuterio reactants, as well as radical inhibition experiments, provided mechanistic insight. Also, an understanding of the relative reactivities of ethers was obtained by pairwise competitions with 4(3H)-quinazolinone.