A new cascade alkoxycarbonylation/cyclization reaction of heterocycle-bearing unactivated alkenes is disclosed. The transformation is mediated by silver carbonate under photoirradiation. This method provides efficient access to pharmaceutically valuable molecules and natural product analogues containing quinazolinone-fused esters. Furthermore, this protocol is compatible with a variety of quinazolinone-bearing unactivated alkenes and alkyloxalyl chlorides that are readily prepared from abundant alcohols and oxalyl chlorides.