Palladium-Catalyzed [4 + 2] Cycloaddition of o-(Silylmethyl)benzyl Esters with Ketones: An Equivalent to Oxo-Diels-Alder Reaction of o-Xylylenes

o-(Silylmethyl)benzyl carbonates reacted with various electron-deficient ketones in the presence of a palladium catalyst, affording the [4 + 2] cycloaddition products, isochromanes, in high yields. The palladium-catalyzed cycloaddition is equivalent to the oxo-Diels Alder reaction of o-xylylene with ketones. The regioselectivities were extraordinarily affected by the structures of the o-xylylene precursors and ketones. The unusual regiochemistry may support two competitive reaction pathways in the catalytic reaction.