Synthesis of Functionalized α,α-Disubstituted β-Alkynyl Esters from Allenoates through an Alkynylenolate Intermediate

Highly substituted alpha,alpha-disubstituted beta-alkynyl esters are readily prepared from allenyl esters and either alkyl halide, acid chloride, or alkyl chloroformate, mediated by an amide base. This highly efficient and mild process tolerates various functional groups and provides alpha,alpha-disubstituted beta-alkynyl esters in good to excellent yields. This method is especially suitable for the synthesis of 1,n-enynes or 1,n-diynes (n > 4). Electrophilic cyclization of 1,5-enyne gives a highly functionalized gamma-iodolactone, whereas its platinum-catalyzed cycloisomerization affords 1,3-cyclohexadiene.