Asymmetric [3+3] Cycloaddition of Trimethylenemethane with Nitrones

Significance

Previously, Trost et al. have reported the use of phosphoramidite ligands in the palladium-catalyzed asymmetric [3+2] cycloaddition of trimethylenemethane derivatives (J. Am. Chem. Soc. 2006, 128, 13328). For the first time, the authors report the corresponding asymmetric [3+3] cycloaddition reaction. Cycloadducts 3 were obtained in high yields and with high ee values with good dia­stereoselectivities. The absence of cycloadducts 4 and 5 led the authors to postulate that the initially formed Pd-TMM intermediate A rapidly isomerizes to give B, having a more stabilized benzylic anion, which subsequently undergoes cycloaddition with 2 to give 3.