The synthesis of allenic acids and esters and their conversion to butenolides has been examined in some detail. Racemic butenolides 10 are efficiently prepared from the esters 8 through treatment with BCl3 and exposure of the derived acid 9 to catalytic AgNO3 in acetone. Conversion of the enantioenriched allenylstannane (S)-17 to the acid 18 through lithiation and subsequent carboxylation with CO2 afforded racemic product. The ...
