(Benzylthio)‐ und (Arylthio)‐substituierte Nitril‐ylide: Thermische Erzeugung und Reaktionen

Thermal Generation and Reactions of (Benzylthio)‐and (Arylthio)‐Substituted Nitrile Ylides Thermolysis of 4‐(benzylthio)‐ and 4‐(arylthio)‐1,3‐oxazol‐5(2H)‐ones 6, at 110–155° in the presence of dipolarophiles with activated C≡C, CC, CO, CS, and NN bonds, led to 5‐membered cyclo‐adducts and CO2 (cf. Schemes 3, 5‐7). Heating 6a and 6c in the presence of ethyl propiolate yielded ethyl quinoline‐3‐carboxylate (19) and ethyl pyridine‐3‐carboxylate(22), respectively (cf. Scheme 8). These results are rationalized on the basis of the intermediate formation of thio‐substituted nitrile ylides of type 7 (cf. Scheme 2), which undergo regioselective 1,3‐dipolar cycloadditions with reactive dipolarophiles. In the absence of such a dipolarophile, the nitrile ylides isomerize via a [1,4]‐H shift to give 2‐aza‐1,3‐butadienes of type 20. The latter are trapped in a Diels‐Alder reaction with ethyl propiolate (cf. Scheme 8).