Asymmetric Formal Abnormal Claisen Rearrangement Enabled by Rh-Catalyzed Regio- and Enantioselective Allylic Alkylation

Abnormal Claisen rearrangement of phenyl allyl ether with the γ-alkyl group is longstanding. However, the asymmetric version of this named reaction has never been reported. Herein, a highly regio- and enantioselective allylic alkylation of 4-hydroxycoumarin and stereospecific Conia-ene/ene sequence has been developed as a formal abnormal Claisen rearrangement. Chiral 4-hydroxycoumarins with 3-allyl groups could be synthesized in up to 95% yield and 96% ee under the catalysis of Rh and chiral bioxazolinephosphine ligand. Experimental and density functional theory calculation investigations support that the stereospecific rearrangement is based on the reversible formation of the kinetically favored cis-disubstituted spirocyclopropane intermediate.