In this paper, a chiral guanidine-catalyzed 1,4-addition reaction of 5H-oxazol-4-ones to allenic esters and ketones is described. 5H-Oxazol-4-ones substituted with a 2-chlorophenyl group were suitable pronucleophiles that gave high enantioselectivities. Subsequent hydrolysis of the obtained adduct gave the corresponding gamma-butenolide ester without loss of enantiopurity and was transformed into (+)-crobarbatic acid in a few steps.