A NEW ALDOL CONDENSATION OF ALPHA-ALLENIC ESTERS WITH ALDEHYDES, INCLUDING A ONE-POT SYNTHESIS OF ENYNE COMPOUNDS

DABCO-catalyzed condensations of ethyl 2,3-butadienoate (1a) with aldehydes at -6 to 25-degrees-C gave 3-hydroxy-2-vinylidenealkanoates 3 in 41-54% yields. Butyllithium-promoted condensations of 1a with aldehydes at -105 to -70-degrees-C afforded 3 in 56-67% yields. Reaction of ethyl 2,3-hexadienoate (1k) with 1-heptanal in the presence of butyllithium gave ethyl 3-hydroxy-2-(1-butenylidene)nonanoate (3k) in 64 % yield; however, when the butyllithium-promoted condensation of 1k with aldehydes was carried out at -90 to -70-degrees-C and then treated in the same pot with wet THF for 11-27 h at room temperature, ethyl (E)-2-(1-alkynyl)-2-alkenoates 7 (12-36% yields) were obtained along with 3 (14-26% yields).