The rhodium-catalyzed N-H and O-H insertion of amides and carboxylic acids with α-diazo-β-ketoesters to give different α-amido- and α-carboxylic-β-ketoesters is presented. Investigations were carried out to establish an efficient N-H and O-H insertion reaction using a range of different amides and carboxylic acids for the synthesis of intermediates e.g. for receptor antagonists. The reactions were performed under mild conditions with 1 mol% of catalyst and the products were formed in good yields.