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The 2,4-dinitrophenylhydrazone (2a) of allyl 2-chloroacetoacetate has been prepared and converted into the azoalkene (4a) by reaction with sodium carbonate. The azoalkene undergoes an intramolecular Diets-Alder reaction when heated under reflux in toluene to give a single product, the cis-fused lactone (5a). Several other allylic esters of ethyl 2-chloroacetoacetate undergo the same sequence of reactions. Evidence is presented that the cis-fused lactones are the kinetic products of intramolecular cycloaddition; the reactions are proposed to involve endo addition of E-azoalkenes. Cyclic azoalkenes (1 6) and ( 20), of the same general type but constrained to the Z configuration, have been prepared starting from allyl 2oxocyclopentane-and allyl 2-oxocyclohexane-1 -carboxylates. These also undergo an intramolecular Diels-Alder reaction when heated. Conjugated azoalkenes bearing an alkoxycarbonyl substituent at the P-position are isolable, and in many cases thermally stable, compounds which undergo a number of different types of cycloaddition reaction. Examples of [2 + 21 and [3 + 21 cycloaddition have been reported,' but the most common type of reaction is a [4 + 21 process in which the azoalkene acts as the 4x component. Such reactions normally require electron rich alkenes (enol ethers, etc.) as the dienophilic components.2We have now investigated intramolecular counterparts of these reactions in which the dienophile is the double bond of an allyloxycarbonyl substituent. This process is outlined in Scheme 1. The objectives of the work have been (i) to determine whether such intramolecular tional activation of

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The azoalkenes (IV) are prepared from the hydrazides (I) and α‐halo ketones (II) via the intermediate hydrazones (III).