Synthesis of ethyl cyclopropenecarboxylates with a leaving group on the position α to the double bond has been realised by photolytic or thermocatalytic decomposition of ethyl diazoacetate with acetylenic substrates. With these adducts allenic, a etylenic or dienic esters are obtained. In the case of photolytic transfer, the proposed intermediate agent is ethoxycarbonyl carbene. If the transfer is thermocatalytic, addition of ethyldiazoacetate to ...