Catalytic Access to Succinimide Products Containing Stereogenic Quaternary Carbons

Enantioselective alpha-branched aldehyde Michael addition toN-phenylmaleimide resulting in non-stereogenic quaternary carbon containing succinimides is common. Here we emphasize the use ofN-benzylmaleimide with a focus on stereogenic quaternary carbon formation. In particular, the potassium carboxylate salt of either L-isoleucine (L-isoLeu) or O-tBu-L-threonine (O-t-Bu-L-Thr), 5.0 mol %, proved effective for the formation of alpha-quaternary-beta-tertiary aldehydic succinimide products in high isolated yield (80-97 %) and excellent enantioselectivity (90-99 %). Furthermore, a carbon-substituted maleimide electrophile has enabled the first example of alpha-quaternary carbon formation with beta- and gamma-stereogenic center formation in 98 %ee, albeit in 40 % yield (product17). From the thirteen formed products, six are reported here for the first time.