Ethyl 2-butynoate, a 2-alkynoate is a methanogenesis inhibitor. It is an electron deficient internal alkyne that has been reported to undergo codimerization with alkenes to form 1,3-dienes catalyzed by rhodium(I)/H8-BINAP complex. The annulation of thioamides with ethyl 2-butynoate catalyzed by tri-n-butylphosphine to form thiazolines has been investigated.