A one-pot multistep methodology leading to trifluoromethylated cyclopenta[c]isoquinolines, indeno[1,2-c]isoquinolines, 6,6-difluoro-1,3-oxazines, or 1,3-oxazin-6-ones, based on the reaction of 5-acylated N-pentafluoroethyl-substituted 1,2,3-triazoles is presented. A thermal ring opening of the starting triazoles, followed by a 1,2-acyl shift formed reactive ketenimines which cyclized after a rearrangement in a substrate-specific manner to provide new trifluoromethylated heterocyclic products.

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.

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.

The front cover picture illustrates the reaction of N-fluoroalkylated-1,2,3-triazoles with aluminum trihalide, proceeding via a vinyl cation (illustrated as the structure in brackets in the middle) to afford structurally diverse N-haloalkenyl imidoyl halides. These products are formed in a stereoselective fashion on both double bonds and have been utilized in the synthesis of various N-alkenyl compounds, such as enamides, enamidines, enimines, N-alkenyl tetrazoles, and other. In this work, Beier and co-workers show a new, mild and efficient 1,2,3-triazole denitrogenative ring-opening process mediated by easily available Lewis acids. Details can be found in the Full Paper by Beier and co-workers (A. Markos, L. Janecký, T. Chvojka, T. Martinek, H. Martinez-Seara, B. Klepetářová, P. Beier, Adv. Synth. Catal. 2021, 363, 3258–3266; DOI: 10.1002/adsc.202100009).

N-Alkenyl compounds are versatile synthetic building blocks and their stereoselective transformations are key processes in the synthesis of many prominent classes of natural products, pharmaceuticals, and agrochemicals. However, a large structural variety of known N-alkenyl compounds and their diverse reactivity have so far precluded the development of a general method for their stereoselective synthesis. Herein we present an aluminum halide-mediated, highly stereoselective, efficient and scalable transformation of commercially available N-fluoroalkyl-1,2,3-triazoles to N-haloalkenyl imidoyl halides, and demonstrate their use in the synthesis of stereodefined N-alkenyl amides, amidines, imines, hydrazonoamides, imidothioates, iminophosphonates, 1,2,4-triazoles and tetrazoles. The reaction is of wide scope on both the triazole substrate and aluminum halide, providing highly functionalized products. Mechanistic and computational investigations suggest a reaction mechanism involving the triazole ring opening, initiated by the coordination of nitrogen one of the triazole ring to the Lewis acid, N-2 elimination and the formation of a vinyl cation intermediate, which reacts with nitrogen-bound aluminum halide, followed by a series of halide exchange reactions on C-X and Al-X bonds.

A reaction of N-sulfonyl-1,2,3-triazole with boron trifluoride etherate afforded a (Z)-β-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)-β-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.