Regioselective α-Addition of Deconjugated γ-Butenolides: Synthesis of Functionalized Dihydroquinolinones

Regioselective reactions of γ-butenolides and the activation of an unactivated α-position represent a significant field of γ-butenolide chemistry. Compared with γ-addition, the regioselective α-addition of γ-butenolides has rarely been exploited. In this study, a regioselective Michael addition/esterification reaction of γ-butenolides with <i>o</i>-amino <i>p</i>-Quinone Methides (QMs) was generated, affording a series of functionalized dihydroquinolinones in high yields with excellent diastereoeselectivities. The studies based on density functional theory (DFT) calculations show that the observed α-regioselectivity can be attributed to steric repulsion between the base and the electrophilic <i>o</i>-amino <i>p</i>-QMs. This research is expected to provide unusual α-addition chemistry of γ-butenolides and novel synthetic methods for dihydroquinolones.