Preparation of New Nitrogen-Bridged Heterocycles. 42.1 Synthesis and the Reaction of Pyridinium N-Ylides Using Bifunctional Ethyl Thiocyanatoacetates

Article abstract of DOI:10.1246/bcsj.69.1769

Various pyridinium (monosubstituted methylide)s were smoothly attacked to the cyano group in ethyl thiocyanatoacetate or ethyl 2-thiocyanatopropionate to afford the corresponding pyridinium (substituted cyanomethylide)s in low-to-moderate yields, while pyridinium (unsubstituted amidate)s reacted with the ester carbonyl group in the same reagents to give pyridinium (thiocyanatoaceto)- or (2-thiocyanatopropiono)amidates in considerable yields. The 1,3-dipolar cycloadditions of some pyridinium (unsymmetrically substituted cyanomethylide)s with dimethyl acetylenedicarboxylate (DMAD) in various solvents afforded only dimethyl 3-cyanoindolizine-1,2-dicarboxylate, except a few examples. On the other hand, the treatment of pyridinium (thiocyanatoaceto)- or (2-thiocyanatopropiono)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 intermediacy of N-[1-(2-thiocyanatopyridinio)]acetamidates in the formation reactions of the latter compounds was also proven by independent syntheses.