Intramolecular cycloaddition of azoalkenes derived from allylic β-keto esters

Abstract

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 (16) and (20), of the same general type but constrained to the Z configuration, have been prepared starting from allyl 2-oxocyclopentane- and allyl 2-oxocyclohexane-1-carboxylates. These also undergo an intramolecular Diets–Alder reaction when heated.