A series of ten aryl-triazole-functionalized boranes bearing BMes2-groups and capable of forming intramolecular five-membered N→B-coordinated heterocycles, has been prepared by 1,3-dipolar cycloaddition.

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.

The heterocyclic mesoionic compound (1,4-diphenyl-1H-1,2,4-triazol-4-ium-3-yl)(phenyl)amide („Nitron“) has recently been found to exist in a prototropic equilibrium with minor amounts of a nucleophilic heterocyclic carbene of the 1,2,4-triazolyl-5-ylidene type. Here we report that Nitron reacts with 1-trifluoromethyl-substituted prop-2-yne iminium salts by conjugate nucleophilic addition of the anionic PhN‒ substituent in the mesoionic tautomer, whereas the nucleophilic triazolylidene form is involved in the reaction with 1-CF3-prop-2-yne imines. 3-(2,3-Dihydro-1H-benzo[c]azepin-5-yl)-1H-1,2,4-triazol-4-ium triflate salts were obtained in the former case and (Z)-9-arylidene-1,2,4,7-tetraazaspiro[4.4]nona-2,7-dienes in the latter.