1,3-Dipolare Cycloadditionen eines Carbonyl-ylids mit 1,3-Thiazol-5(4H)-thionen und Thioketonen

1,3-Dipolar Cycloadditions of a Carhonyl-ylide with 1,3-Thiazole-5(4H)-thiones and Thioketones Inp-xylene at 150°, 3-phenyloxirane-2,2-dicarbonitrile ( 4b ) and 2-phenyl-3-thia-1-azaspiro4.4]non-1-ene-4-thione ( 1a ) gave the three 1:1 adduets trans- 3a , cis- 3a , and 13a in 61, 21, and 3% yield, respectively (Scheme 3). The stereoisomers trans- 3a and cis- 3a are the products of a regioselective 1,3-dipolar cycloaddition of carbonylylide 2b , generated thermally by an electrocyclic ring opening of 4b (Scheme 6), and the C?S group of 1a . Surprisingly, 13a proved not to be a regioisomeric cycloadduct of 1a and 2b , but an isomer formed via cleavage of the O? C(3) bond of the oxirane 4b . A reaction mechanism rationalizing the formation of 13a is proposed in Scheme 6. Analogous results were obtained from the reaction of 4b and 4,4-dimethyl-2-phenyl-1,3-thiazole-5 (4H)-thione ( 1b , Scheme 3). The thermolysis of 4b in p-xylene at 130° in the presence of adamantine–thione ( 10 ) led to two isomeric 1:1 adducts 15 and 16 in a ratio of ca. 2:1, however, in low yield (Scheme 4). Most likely the products are again formed viathe two competing reaction mechanisms depicted in Scheme 6. The analogous reactions of 4b with 2,2,4,4-tetramethylcyclobutane-1,3-thione ( 11 ) and 9H-xanthene-9-thione ( 12 ) yielded a single 1:1 adduct in each case (Schemes). In the former case, spirocyclic 1,3-oxathiolane 17 , the product of the 1,3-dipolar cycloaddition with 2a corresponding to 3a , was isolated in only 11 % yield. It is remarkable that no 2:1 adduct was formed even in the presence of an excess of 4b. In contrast, 4b and 12 reacted smoothly to give 18 in 81 % yield; no cycloadduct of the carbonylylide 2a could be detected. The structures of cis- 3a , 13a , 15 , and 18 , as well as the structure of 14 , which is a derivative of trans- 3a , have been established by X-ray crystallography (Figs. 1–3, Table).