An asymmetric I,4-addition reaction of 5H-oxazol-4-ones with alkynyl carbonyl compounds was developed, and, for the first time, high enantiomeric and geometric control was achieved to afford the thermodynamically unstable Z-isomer predominantly using chiral guanidine catalysts bearing a hydroxy group at the appropriate position. The method provides synthetically useful gamma-butenolide ester bearing a chiral quaternary stereogenic center.