A convenient Fe-catalyzed decarbonylative alkylation–peroxidation of alkenes with aliphatic aldehydes and TBHP to provide chain elongated peroxides is developed, which is further applied to the one-pot synthesis of alkylated ketones. Aliphatic aldehydes were decarbonylated into 1°, 2° and 3° alkyl radicals at low temperature which subsequently allows the cascade construction of C(sp³)–C(sp³) and C(sp³)–O bonds via radical insertion and radical–radical coupling. Various alkenes including mono-substituted, terminally disubstituted or internally disubstituted styrenes bearing synthetically useful functional groups and electron-poor acrylates were tolerated.