Cycloaddition Behavior of Cyclopentadienone toward Allylic Alcohols.Formation of Hydrophthalide Derivatives via Internal Addition of Alcohol Group to Bridged Carbonyl of exo [4+2]π Cycloadducts

Abstract

The cycloaddition behavior of 2, 5-bis(methoxycarbonyl)-3, 4-diphenylcyclopentadienone (Ia) toward allylic alcohols(II) was investigated. The exo [4+2]π cycloadducts were transformed into hydrophthalide derivatives via intramolecular addition of the alcohol group to the strained bridged carbonyl. The endo [4+2]π cycloadducts underwent transesterification with the bridgehead methoxycarbonyl group to give the lactone derivatives. The structures of the products were determined on the basis of the ¹H- and ¹³C-NMR spectral data and X-ray analyses. The reactivity of Ia toward allylic alcohols is discussed in terms of frontier molecular orbital (FMO) theory.