levo-2,3-Butanediol will condense with ethyl acetoacetate in the presence of hydrochloric acid to give the ethyl ester oflevo-2,4,5-trimethyl-2-carboxymethyl-1,3-dioxacyclopentane (I) (yield 48%) from which the free acid may be obtained. Ifp-toluenesulphonic acid is used as the catalyst and the condensation is carried out in boiling butanol with continuous removal of water, the butyl ester of (I) is obtained (yield 87%). Compounds described for the first time arelevo-,dl-, andmeso-2,4,5-trimethyl-2-carboxymethyl-1,3-dioxacyclopentanes, theirn-butyl andp-bromophenacyl esters (melting points 74.5°, 76°, and 76 °C., respectively) and the ethyl ester of thelevo-isomer.