Palladium-Catalyzed Asymmetric Allylic Alkylation of Cyclic Dienol Carbonates: Efficient Route to Enantioenriched γ-Butenolides Bearing an All-Carbon α-Quaternary Stereogenic Center
Allyl dienol carbonates (1) served as substrates for the title reaction to afford the furanones 2 in both high yields and high enantioselectivities. These furanones were eventually converted into valuable buildingblocks including γ‐tertiary and γ‐quaternary furanones (3) as well as β‐quaternary butyrolactones (4). This method was used as a key step in the totalsynthesis of (−)‐nephrosteranic acid
AuCl3 efficiently catalyzes cyclization of tert-butyl allenoates into γ-butenolides. Advantage of directly using allenic ester precursor instead of corresponding acid is demonstrated in the synthesis of a variety of 2,4-disubstituted butenolides. A low catalyst loading and mild reaction condition makes this process an attractive alternative over conventional methods using strong Lewis acids.