Cycloaddition Reactions of 2-Ethoxyisobutenylidenecyclopropane and 2,3-Tetramethyleneisobutenylidenecyclopropane

Article abstract of DOI:10.1021/jo01298a047

The title compounds (15 and 6) were reacted with maleic anhydride and N-phenylmaleimide (7a and 7b) in an attempt to derive cycloaddition across the "methylenecyclopropane" portions of 6 and 15 in a manner previously observed with 4-phenyl-1,2,4-triazoline-3,5-dione.Cycloaddition in the desired manner did not occur.Instead, 6 reacted with 7a and 7b to give predominantly ene product (which underwent further cycloaddition) along with <2 + 2> cycloaddition across the exocyclic double bond.To a minor extent 6 also underwent <1,3> sigmatropic rearrangement followed by cycloaddition. 15 underwent only sigmatropic rearrangement followed by cycloaddition of the intermediate diene with 7b.Reasons for the observed differences in reactivity and mode of reaction are discussed on the basis of the effect of the ethoxy group of 15 on the orbital energies as determined by photoelectron spectroscopy and theoretical calculations.