Reaction of ketenes. Part 18. Catalysed reactions between α-diazocarbonyl compounds and ketene acetals

In the presence of copper powder or Cu(acac)2, ethyl diazoacetate reacts with dialkylketene acetals to give cyclopropanes (2) whilst with ketene acetals having at least one hydrogen atom at position 2 both cyclopropanes (2) and butenoates (3) are formed. Noteworthy in these reactions is the fact that the α-diazoester fails to give dihydrofurans (1), which are the only reaction products when α-diazoketones are the employed α-diazocarbonyl compounds. The results can be rationalized on the basis of the intermediacy of a species in which α-diazocarbonyl compound, catalyst, and ketene acetal are involved.