[reaction: see text] L-proline failed to act as an organocatalyst in the homoaldol reaction of ethyl pyruvate; however, it reacted with the ester to give an azomethine ylide that in turn underwent 1,3-dipolar cycloaddition with a second molecule of pyruvate. Direct catalytic homoaldol reaction of ethyl pyruvate was performed using an (S)-(+)-1-(2-pyrrodinylmethyl)pyrrolidine/trifluoroacetic acid combination as organocatalyst. The use of polymer-supported reagents allowed for the lactonization of the aldol and isolation of the isotetronic acid derivative in hydroxy-free form.