Novel cycloaddition reactions of o-benzoquinones and related chemistry

Abstract

o-Benzoquinone is a unique conjugated 1,2-dione that can exhibit diverse cycloaddition modes, participating either as carbodiene, helcrodiene, dienophile or heterodienophile. With electron-rich dienes, bcnzodioxins are formed in excellent yields. Pentafulvenes including 6-vinylfulvenes normally give rise to bicyclo [2.2.2] adducts. Exceptions are observed with cycloalkylfulvenes where the fulvenes undergo rearrangement to cyclopentadiene derivatives prior to cycloaddition, resulting in benzodioxins. o-Benzoquinones participate as dipolarophiles on treatment with nitrile oxides and carbonyl ylides yielding highly oxygenated novel spiro compounds. Triphenylphosphine catalyzed addition of DMAD to o-benzoquinones afforded another class of novel spirolactones. The bicyclo [2.12] octene diones derived from o-benzoquinones undergo a number of synthetically useful transformations. ©Indian Academy of Sciences.