In a preliminary communication (1, 2) the reaction of two representative ketones, benzophenone and fluorenone, with diethyl methylsuccinate in the presence of sodiunl ethoxide was shown to proceed by a Stobbe condensation giving the expected half-esters in good yields. In the present work we are reporting an extension of this study on both aldehydes and ketones. Benzaldehyde, o-methoxybenzaldehyde, p-chlorobenzaldehyde, benzophenone, and acetophenone were condensed with dimethyl methylsuccinate in the presence of potassium tert-butoxide (3); froin the products were formed anhydrides, half-esters, indones, and naphthalene derivatives. In all these reactions, exact parallels were found with the corresponding products previously obtained from ethyl succinate itself (3).Good yields (60-72%) of the P-half-esters (11) were obtained from the condensation of benzaldehyde, o-methoxybenzaldehyde, benzophenone, and acetophenone. However, the yield was only poor, as expected, with p-chlorobenzaldehyde, but a shorter period of reflux was found to increase this yield slightly and minimize resinification. In the case of acetophenone, the isomeric P-half-ester (VI; R = CH3) was also obtained and separated.The condensation of the aldehydes in general afforded, in addition to the expected half-esters, varying amounts of the corresponding itaconic acids. o-Methoxybenzaldehyde gave also a small amount of an acidic non-ketonic substance, m.p. 217", which was found to be the lactonic acid (IX). The constitution of (IX) as 2-o-anisyl-3-carboxy-4-o-methoxybenzylidene-3-methyl-5-oxotetrahydrofuran follows from the following observations: (a) the infrared spectrum (KBr) showed a strong band a t 1750 cm-I, characteristic of the stretching frequencies of carbonyl groups of a,punsaturated-y-lactones (4) and (b) alkaline hydrolysis of the substance gave the itaconic acid (11; R1 = R3 = Rq = H, Rz = CH3O) and o-methoxybenzaldehyde which was characterized as the 2,4-dinitrophenylhydrazone. Analogs of (IX) have frequently been observed in the condensations of ethyl succinate with aromatic aldehydes. The formation of this lactonic acid a t high temperature is evidence for (a) the relative stability of the intermediate paraconic ester (3) towards the tert-butoxide ions; and (b) the comparative reactivity of o-methoxybenzaldehyde. When o-rnethoxybenzaldehyde was condensed with dimethyl methylsuccinate in the presence of sodium ethoxide a t -15O, the lactonic acid (IX) was obtained as the main product.