Regioselective α‐Addition of Deconjugated Butenolides: Enantioselective Synthesis of Dihydrocoumarins

The enantioselective α‐addition of deconjugated butenolides has rarely been exploited, in contrast to the well‐studied γ‐addition of deconjugated butenolides. In this study, an unprecedented asymmetric α‐addition/transesterification of deconjugated butenolides with ortho ‐quinone methides generated in situ afforded a series of functionalized 3,4‐dihydrocoumarins containing two contiguous stereogenic centers with excellent diastereo‐ and enantioselectivity. DFT calculations suggested that the rarely observed regioselectivity was due to the distortion energy that resulted from the interaction between the nucleophilic dienolate and the electrophilic ortho ‐quinone methide.