Ethyl 5-Chloro-2-oxopent-3-ynoate, a New Acetylenic Dienophile in the Diels—Alder Reactions.

Treatment of the lithium salt of propargyl chloride (I) with diethyl oxalate (II) at low temperatures under strictly controlled conditions provides the previously unknown ester (III) which undergoes Diels—Alder reactions with conjugated dienes.