Diastereoselective Synthesis of Rauhut–Currier-Type Adducts via an Unexpected α‑Addition of α,β-Unsaturated γ‑Butyrolactams to Coumarin Derivatives

A novel, base-catalyzed and highly
diastereoselective direct Michael
addition-isomerization sequence is presented for the efficient synthesis
of Rauhut–Currier-type adducts. An unexpected α-addition
of γ-butyrolactam onto the 3-acyl coumarin derivatives was observed
rather than the γ-addition, which is more common. The adducts
could further undergo hydrolysis/decarboxylation to generate the products
which are equivalent to those obtained by α-addition of γ-butyrolactam
onto the corresponding chalcones.