Methyl diazoacetoacetate undergoes zinc triflate catalyzed condensation with a broad selection of aldehydes to produce delta-siloxy-alpha-diazo-beta-ketoalkanoates in good yield, and delta-hydroxy-alpha-diazo-beta-ketoalkanoates are formed with high diastereoselectivity in reactions with alpha-diazo-beta-ketopentanoate promoted by dibutylboron triflate.