Novel cycloaddition reactions of o-benzoquinones and related chemistry

o-Benzoquinone is a unique conjugated 1,2-dione that can exhibit diverse cy cloaddition modes, participating either as carbodiene, heterodiene, dienoph ile or heterodienophile. With electron-rich dienes, benzodioxins are formed in excellent yields. Pentafulvenes including 6-vinylfulvenes normally give rise to bicyclo[2.2.2] adducts. Exceptions are observed with cycloalkylful venes where the fulvenes undergo rearrangement to cyclopentadiene derivativ es prior to cycloaddition, resulting in benzodioxins. o-Benzoquinones parti cipate as dipolarophiles on treatment with nitrile oxides and carbonyl ylid es yielding highly oxygenated novel spiro compounds. Triphenylphosphine cat alyzed addition of DMAD to o-benzoquinones afforded another class of novel spirolactones. The bicyclo [2.2.2] octene diones derived from o-benzoquinon es undergo a number of synthetically useful transformations.