Palladium-Catalyzed[3+2]Cycloaddition of Trimethylenemethane with p-Benzoquinones

The reaction of trimethylenemethane with various alkyl-substituted p-benzoquinones was investigated. The reaction of 2, 5-di-tert-butyl-p-benzoquinone with 2-(trimethylsilylmethyl)allyl acetate(1) was conducted with palladium(0) as a catalyst to afford 1:1-C=C-cycloadduct 2 in good yield. Similarly, 1:1-C=C-cycloadducts 3, 4, 5 and 6 were obtained with 2, 6-di-tert-butyl-p-benzoquinone, 2, 3, 5, 6-tetramethyl-p-benzoquinone, 2, 3, 5-trimethyl-p-benzoquinone and 2-methyl-1, 4-naphthoquinone, respectively. On the other hand, the reaction with methyl-p-benzoquinone afforded the complicated mixture. As is the case with Diels-Alder reactions, the cycloaddition of trimethylenemethane with p-benzoquiones occurred towards C-C double bond. So, the reaction of trimethylenemethane with substituted p-benzoquinones is effective in the synthesis of methylenecyclopentane-fused cyclohexenediones having various substituents.