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‐CF 3 ‐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 C 2 +C 3 ‐CF 3 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 CF 3 ‐containing compounds with cyclopenta[ b ]furan, cyclopenta[ b ]thiophene, cyclopenta[ c ]thiophene, cyclopenta[ b ]pyrrole, cyclopenta[ c ]pyrrole, 3 H ‐pyrrolizine, and 1,4‐dihydrocyclopenta[ b ]pyrrole ring systems. Analogous reactions of 1,3(or 1,4)‐phenylenebis(1‐CF 3 ‐propyne iminium) salts with furans, pyrroles or thiophenes in a 2 : 1 stoichiometry lead to phenylene‐tethered condensed heterocycles of the same type.