Stabilization, isomerization and rearrangement of enyne [4 + 4]-cycloadducts.

Reactive 1,2,5-cyclooctatrienes, formed by photocycloaddition of 2-pyridones with enynes, are stabilized by steric shielding, slowing or preventing an otherwise facile [2 + 2]-dimerization reaction. Diisopropylsilyl ether-tethered reactants paired with an alkene substituent (R) produce allenes that are stable (R = TMS) or that isomerize to 1,3-dienes by hydrogen migration (R = alkyl). Under acidic conditions, hydrolysis of the photoproduct's silyl ether can lead to a [3,3]-sigmatropic rearrangement.