Abstract Diazo sulfones, diazo phosphine oxides, and diazo phosphonates add to aldehydes in the presence of a catalytic amounts of tin (II) chloride to yield β-keto sulfones, β- keto phosphine oxides, and β-keto phosphonates, respectively. Reactions with primary aldehydes proceed in higher yields, 53–79%, than those of secondary aldehydes, 42–56%. Reactions with tertiary aldehydes, which are more sterically encumbered substrates, give ...