PREPARATION OF NEW NITROGEN-BRIDGED HETEROCYCLES .42. SYNTHESIS AND THE REACTION OF PYRIDINIUM N-YLIDES USING BIFUNCTIONAL ETHYL THIOCYANATOACETATES

Various pyridinium (monosubstituted methylide)s were smoothly attacked to the cyano group in ethyl thiocyanatoacetate or ethyl 2-thiocyanato propionate to afford the corresponding pyridinium (substituted cyanome thylide)s in low-to-moderate yields, while pyridinium (unsubstituted a midate)s reacted with the ester carbonyl group in the same reagents to give pyridinium (thiocyanatoaceto)- or (2-thiocyanatopropiono)amidate s in considerable yields. The 1,3-dipolar cycloadditions of some pyrid inium (unsymmetrically substituted cyanomethylide)s with dimethyl acet ylenedicarboxylate (DMAD) in various solvents afforded only dimethyl 3 -cyanoindolizine-1,2-dicarboxylate, except a few examples. On the othe r hand, the treatment of pyridinium (thiocyanatoaceto)- or (2-thiocyan atopropiono)amidates with a strong base, such as potassium t-butoxide, gave new bicyclic mesoionic compounds, N-[2-(1,3,4-thiadiazolo [3,2-a ]pyridinio)]acetamidate derivatives, in moderate yields. The intermedi acy of N-[1-(2-thiocyanatopyridinio)] acetamidates in the formation re actions of the latter compounds was also proven by independent synthes es.