Synthesis of (E)- and (Z)-α-Alkylidene-γ-aryl-γ-butyrolactones via Alkenylalumination of Oxiranes

Alkenylalumination of substituted styrene oxides with [α-(ethoxycarbonyl)alkenyl]diisobutylaluminum, in the presence of BF3·Et2O, affords the corresponding (Z)-α-alkylidene-γ-aryl-γ-hydroxy esters in 81−100% Z-selectivity. Chromatographic separation of isomers, followed by lactonization with trifluoroacetic acid, provides isomerically pure (Z)-α-alkylidene-γ-aryl-γ-butyrolactones in 53−78% overall yield. Isomerization of the (Z)-alkylidene hydroxyl esters using LDA, followed by protonation using a bulky proton source, such as BHT, provides a simple route to the corresponding α-(E)-alkylidene-γ-phenyl-γ-hydroxy esters in 72−78% yield, which were cyclized to obtain the corresponding (E)-butyrolactones in 78−85% yield.