Lewis acid-mediated transformations of 5-acyl-N-fluoroalkyl-1,2,3-triazoles to cyclopentenones, indenones, or oxazoles.

We present a transition metal-free approach to 2-N-substituted indenones, cyclopentenones, and 4-carbonyl oxazoles, based on the reaction of 5-acylated N-fluoroalkyl substituted 1,2,3-triazoles (prepared by a three-component click reaction of copper acetylides, fluoroalkyl azides, and acyl chlorides) with Lewis acids aluminium trichloride or boron trifluoride etherate, proceeding via the generation and cyclization of vinyl cations.

Lewis-Acid-Mediated Intramolecular Cyclization of 4-Aryl-5-allyl-1,2,3-triazoles to Substituted Cyclopentene Derivatives.

4-Aryl-5-allyl-N-fluoroalkyl-1,2,3-triazoles available by a three-component reaction of fluoroalkyl azides, copper acetylides, and allyl halides underwent aluminum halide-mediated transformation to N-(4-halo-2-aryl-cyclopentenyl) imidoyl halides by cyclization of vinyl cation intermediates, followed by halide capture. Utilization of the cyclic products was demonstrated by the synthesis of N-alkenyl amides, amidines, isoquinolines, and tetrazoles or by the subsequent modification of the cyclopentene ring.

Stereoselective Synthesis of (Z)-ß-Enamido Fluorides from N-Fluoroalkyl- and N-Sulfonyl-1,2,3-triazoles.

A reaction of N-sulfonyl-1,2,3-triazole with boron trifluoride etherate afforded a (Z)-ß-ensulfonylamido fluoride instead of the previously erroneously assigned E isomer. The correction of the stereochemistry was based on a ge-1D ROESY NMR experiment and X-ray crystal structure analyses. Application of the reaction to N-fluoroalkyl-1,2,3-triazoles afforded new (Z)-ß-enamido fluorides in a stereoselective manner. A mechanism involving coordination of BF3 with the triazole ring and vinyl diazonium and vinyl cation intermediates was proposed.