Taking diazo transfer to water: α-diazo carbonyl compounds from in situ generated mesyl azide

Mesyl azide generated in situ in aqueous medium converted a range of active methylene substrates into the corresponding diazo compounds in good yields and high purity with no need for chromatographic purification. The products thus obtained are suitable for the subsequent Rh^II-catalyzed O–H insertions with no need for chromatography in the interim.