A more robust method for preparing ketenes is the carbonylation of metal-carbenes, and "in situ" reaction of the thus produced highly reactive ketenes with suitable reagents such as imines, amines, or alcohols. This method is an efficient one‐pot tandem protocol of the carbonylation of α‐diazocarbonyl compounds and a variety of "N"‐tosylhydrazones catalysed by Co(II)–porphyrin metalloradicals leading to the formation of ketenes, which subsequently react with a variety of nucleophiles and imines to form esters, amides and β‐lactams. This system has a broad substrate scope and can be applied to various combinations of carbene precursors, nucleophiles and imines.