The chemistry of polyfluorinated azides
In 2017, we reported a breakthrough in azide chemistry. CF3N3 and longer carbon chain analogues were prepared from silanes or other carbanion precursors, which opened a door to study properties and reactivity of these compounds. They are no longer regarded as chemical curiosities. Furthermore, they were shown to be stable and not explosive (Angewandte Chemie International Edition 56: 346, 2017). Subsequently, other fluorinated azides such as HCF2N3 (European Journal of Organic Chemistry 5087, 2018), BrCF2N3, BrCF2CF2N3 (Journal of Organic Chemistry 85: 11482, 2020), RCF2CF2N3 (Organic and Biomolecular Chemistry 15: 4962, 2017) and FCH2N3 (Organic Chemistry Frontiers 7: 10, 2020) were prepared. They readily underwent copper(I)-catalyzed azide-alkyne cycyloadditions (CuAAC) and enamine-mediated azide-ketone cycloadditions (ChemistrySelect 3: 7045, 208) to form novel N-perfluoroalkyl triazoles. Preparation and reactivity of fluorinated azides was recently reviewed (Chemistry – A European Journal 773, 2020).
In the presence of superacids, azidotrifluoromethane protonates on nitrogen one to trifluoromethylamino diazonium cations (CF3NHN2)+ (Angewandte Chemie International Eddition 59: 12520, 2020) (collaboration with University of Southern California).
Heating N-(per)fluoroalkyl triazoles in the presence of rhodium catalyst allows to enter rhodium carbene chemistry for the synthesis of novel N-(per)fluoroalkyl pyrroles, imidazoles, azepines, oxazoles, thiazoles and other heterocycles (Chemical Communications 54: 3258, 2018, Journal of Organic Chemistry 83: 15195, 2018, Organic Chemistry Frontiers 6: 3776, 2019).
A new reactive mode was discovered in N-(per)fluoroalkyl triazoles. In the presence of superacids, such as triflic acid or fluorosulfonic acid, the triazoles ring open and vinyl triflates enamides are formed via a vinyl cation (Chemistry – A European Journal 25: 7640, 2019).
This reactive mode was extended to Lewis acids – in the presence of boron trifluoride β-enamido fluorides are formed (Organic Letters 23: 4224, 2021) and with aluminium halides highly functionalized haloalkenyl imidoyl halides are produced (Advanced Synthesis & Catalysis 363: 3528, 2021).
