By Heck reaction of isoalantolactone with aryl bromides or aryl iodides (3aR,4aS, 8aR,9aR,E)-3-arylmethylidene-8a-methyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-ones and (4aS,8aR,9aS)-3-arylmethyl-8a-methyl-5-methylidene-4a, 5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-ones, products of the double bond shift, were synthesized. The yields of the arylation products depend on the nature of the catalytic system and on the structure of the aryl halide. The structures of (3aR,4aS,8aR,9aR,E)-3-(3,4-dimethoxybenzylidene)-8a-methyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-one and (4aS,8aR,9aS)-3-(2-methylsulfanylbenzyl)-8a-methyl-5-methylidene-4a, 5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b]furan-2(4H)-one were proved by XRD analysis.Compounds containing in their structure an α-methylidene-γ-lactone moiety, in particular, sesquiterpene lactones, attract attention due to their versatile physiological activity, including anticancer action [1]. It was established in the course of the study of structure-activity interrelation in the series of sesquiterpene lactones that the high cytotoxicity correlated with the presence of an exocyclic double bond in the lactone ring [2]. An available lactone of eudesmanic type is isoalantolactone (I), a characteristic metabolite of various species of elecampane Inula sp. [3]; the protocols of its complete synthesis are described both for the racemic [4] and the optically active form [5].In a recent publication [6] we described the fi rst application of Heck reaction to the structural modifi cation of sesquiterpene methylenelactones. Here we report on the C 13 -arylation of isoalantolactone (I).Reaction of compound I with aryl bromides IIa-IId or aryl iodides IIe-IIn catalyzed by the system palladium acetate-phosphine ligand proceeds in DMF in the presesnce of triethylamine. The main reaction products are (3aR,4aS, 8aR,9aR,E)-3-arylmethylidene-8a-methyl-5-methylidenedecahydronaphtho[2,3-b]furan-2(3H)-ones IIIa-IIIn and (4aS,8aR,9aS)-3-arylmethyl-8a-methyl-5-methylidene-4a, 5,6,7,8,8a,9,9a-octahydronaphtho[2,3-b] furan-2(4H)-ones IVb, IVd, IVe-IVl (Scheme 1, Table 1). Compounds IIIa-IIIn, IVe, IVf, IVh, IVj, IVk, IVl were isolated in the individual state by column chromatography on silica gel. The ratio of compounds III and the products IV of the double bond shift will be further shown to depend on such factors as the type and the structure of the aryl halide, the structure of the phosphine ligand and the palladium component of the catalyst. Table 1 compiled the results of experiments on the reaction of isoalantolactone with the aryl halides under the action of the system Pd(OAc) 2 -(o-Tol) 3 P. The fi rst pemittable conclusion consist in the statement of the increase in the yield of isomeric lactones IV at the use of aryl iodides IIe-IIl. The bringing into the reaction of bromo(iodo)arenes IId, IIm, IIn made it possible to obtain only the corresponding lactones IIId, IIIm, IIIn. The minimum yield of isomeric lactones IVa-IVd was obtained in the runs with aryl bromides IIa-II...