Investigations into radical and palladium(0) cyclisations onto the C-2 position of the 3H-quinazolin-4-one moiety have been made. This has led to the syntheses of a number of biologically active quinazolinone natural products using alkyl, heteroaryl and acyl radical cyclisations. The reactions proceeded via a homolytic aromatic substitution mechanism. As such, fully rearomatised products were recovered. A C-2 radical 3H-quinazolin-4-one building block was also prepared. This turned out to have only limited synthetic applications. Radical cyclisations onto aryl groups were carried out using this building block.