Metal substituted diazo esters as substrates for cross coupling reactions

Ethyl (trialkylstannyl)diazoacetates have been employed as substrates in the Stille reaction. The palladium(0)-catalyzed cross coupling works well with aryl iodides but not with acyl or aryl chlorides. Bis-[ethoxycarbonyl-diazomethyl]-mercury showed high reactivity toward bromoacetyl bromide furnishing ethyl 4-bromo-2-diazo-3-oxo-butanoate in excellent yield, This compound was used in substitution reactions with a variety of nucleophiles. The base-promoted reaction of ethyl 4-azido-2-diazo-3-oxo-butanoate with both acetaldehyde and benzaldehyde proceeded in high yield to produce mixed aldol products, The use of an equivalent amount of DABCO was found to be the best way to promote the reaction. The diastereoselectivity exhibited in the reaction is low and characteristic of condensations of alpha-substituted ketones with substituents other than alkyl groups at the alpha-position, Similar consequences were found for the reaction of ethyl 2-diazo-3-oxo-4-phenyl-butanoate with acetaldehyde and benzaldehyde. (C) 1997, Elsevier Science Ltd.