Reactions of a 3‐Phenyl‐1‐trifluoromethyl‐prop‐2‐yne Iminium Salt with Furans, Thiophenes, and Pyrroles

Reactions of a novel propyne iminium salt, N,N‐dimethyl 3‐phenyl‐1‐trifluoromethyl‐propyne iminium triflate, with electron‐rich heteroaromatic ring systems (furans, thiophenes, pyrroles) are reported. The 1‐CF3‐propyne iminium ion can act as a highly reactive ambident electrophile, giving rise to simple electrophilic heteroaromatic ring substitution products, and as a 1,3‐biselectrophile leading to C2+C3‐CF3 annulation products. Moreover, it is an electron‐deficient alkyne which was found to afford double [2+2] cycloaddition products with 2,5‐dimethylfuran and 2,5‐dimethylthiophene. The obtained molecular structures include CF3‐containing compounds with cyclopenta[b]furan, cyclopenta[b]thiophene, cyclopenta[c]thiophene, cyclopenta[b]pyrrole, cyclopenta[c]pyrrole, 3H‐pyrrolizine, and 1,4‐dihydrocyclopenta[b]pyrrole ring systems. Analogous reactions of 1,3(or 1,4)‐phenylenebis(1‐CF3‐propyne iminium) salts with furans, pyrroles or thiophenes in a 2 : 1 stoichiometry lead to phenylene‐tethered condensed heterocycles of the same type. Reactions of a novel propyne iminium salt, N,N‐dimethyl 3‐phenyl‐1‐trifluoromethyl‐propyne iminium triflate, with electron‐rich heteroaromatic ring systems (furans, thiophenes, pyrroles) are reported. The 1‐CF3‐propyne iminium ion can act as a highly reactive ambident electrophile, giving rise to simple electrophilic heteroaromatic ring substitution products, and as a 1,3‐biselectrophile leading to C2+C3‐CF3 annulation products.