The Effect of Lewis Acids on the Cycloaddition of 3,3,6‐Trimethylcyclohex‐5‐ene‐1,2,4‐trione: Hydrogen Transfer versus Cycloaddition with Cyclopentadiene

Abstract Exposure of 3,3,6‐trimethylcyclohex‐5‐ene‐1,2,4‐trione to catalytic amounts of Lewis acids revealed two disparate reactions in the presence of cyclopentadiene. The expected cycloaddition was found to be reversible for the title compound, and transfer hydrogenation was the preferred pathway over long periods of time. Other tested substrates were able to undergo facile cycloaddition with considerable yields and without the parallel reduction.