o-Benzoquinone is a unique conjugated 1,2-dione that can exhibit diverse cycloaddition modes, participating either as carbodiene, heterodiene, dienophile 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 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 too-benzoquinones afforded another class of novel spirolactones. The bicyclo [2.2.] octene diones derived fromo-benzoquinones undergo a number of synthetically useful transformations.