An improved method for the synthesis of 8 [(1E) 2 phenylethenyl]codeinone dimethyl ketal was described. The ability of [(1E) 2 phenylethenyl] substituent to stabilize effectively the π system of the ring C is responsible for the essential difference in both the reactivity and the compositions of products formed in the reactions of the corresponding substituted and unsubsti tuted codeinone and thebaine derivatives. Thevinone (1a) is a key intermediate on the synthetic route from natural alkaloid thebaine (2a) toward orvinols (3a), so called "semi synthetic" opioid derivatives exhibit ing marked affinity to opioid receptors (e.g., buprenor phine, diprenorphine, ethorphine, dihydroethorphine). 1,2 Therefore, compounds 3a for decades are the subjects for intense search for potent analgetics for treatment of severe and chronic pain with decreased level of unwanted side effects. Compound 1a is formed by [4+2] cycloaddition of AcCH=CH 2 to diene system of 2a and serve as the starting compound for the synthesis of large scope of thevinols 3b, O demethylation of the latter leading to compounds 3a. A variety of compounds 3b and 3a resulted mainly from altering the substituents R 2 and R 3 . However, recently, modification of the C(6)-C(14) etheno or ethano bridge of compounds 3 became of interest. Functionalization of these positions can be achieved by either preliminary in troduction of the substituent at the positions 7 or 8 of diene 2a (which correspond to positions 18 and 19 of ad duct 1a) followed by [4+2] cycloaddition 3 or by modifica tion of the ethene bridge in the Diels-Alder adduct. 4,5Recently, in the framework of the design of novel pro cedures for the modification of the C ring of the morphi nan alkaloids, we carried out the Pd catalyzed Heck reac tion of codeine (4a) and PhCH=CHBr to give 7,8 di hydro 8β [(1E) 2 phenylethenyl]codeinone (5a), from which 8 [(1E) 2 phenylethenyl]codeinone dimethyl ket al (6a) was synthesized in four steps. 6 It was found that ketal 6a bearing conjugated diene system reacts with di enophiles to give adducts 7 including 19 [(1E) 2 phenyl ethenyl]thevinone (1b) (in the reaction with AcCH=CH 2 ) instead of the expected 7,8 fused compounds. The use of ketal 6a as "masked" 8 [(1E) 2 phenylethenyl]thebaine (2b) opens the route toward derivatives of compounds 3 substituted at the position 19. Moreover, the hydrolysis of ketal 6a and subsequent reduction of the carbonyl group afforded 8 [(1E) 2 phenylethenyl]codeinone (4b), which in the "ordinary" Diels-Alder reaction gives derivatives with the additional cycle fused to the C ring at the posi tions C(7)-C(8). 6 Thus, ketal 6a is the key intermediate toward both the 7,8 fused derivatives of morphinan alkaloids and de 1, 2: R = H (a), trans CH=CHPh (b) 3: R 1 = H (a), Me (b); Z∼Z = CH 2 CH 2 , CH=CH