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 work s well with aryl iodides but not with acyl or aryl chlorides. Bis-[eth oxycarbonyl-diazomethyl]-mercury showed high reactivity toward bromoac etyl bromide furnishing ethyl 4-bromo-2-diazo-3-oxo-butanoate in excel lent yield, This compound was used in substitution reactions with a va riety of nucleophiles. The base-promoted reaction of ethyl 4-azido-2-d iazo-3-oxo-butanoate with both acetaldehyde and benzaldehyde proceeded in high yield to produce mixed aldol products, The use of an equivale nt amount of DABCO was found to be the best way to promote the reactio n. The diastereoselectivity exhibited in the reaction is low and chara cteristic of condensations of alpha-substituted ketones with substitue nts other than alkyl groups at the alpha-position, Similar consequence s were found for the reaction of ethyl 2-diazo-3-oxo-4-phenyl-butanoat e with acetaldehyde and benzaldehyde. (C) 1997, Elsevier Science Ltd.