1. 4-(4,6-di[2,2,2-trifluoroethoxy]-1,3,5-triazin-2-yl)-4-methylomorpholinium tetrafluoroborate. Triazine-based coupling reagents designed for coupling sterically hindered substrates
Konrad G Jastrzabek, Ramon Subiros-Funosas, Fernando Albericio, Beata Kolesinska, Zbigniew J Kaminski J Org Chem. 2011 Jun 3;76(11):4506-13. doi: 10.1021/jo2002038. Epub 2011 Apr 29.
4-(4,6-Di[2,2,2-trifluoroethoxy]-1,3,5-triazin-2-yl)-4-methylomorpholinium tetrafluoroborate (DFET/NMM/BF(4)) was prepared and used as a reagent for coupling sterically hindered substrates. The formation of the appropriate triazine "superactive" ester in a reaction of DFET/NMM/BF(4) with carboxylic acids was confirmed. The efficiency of the reagent has been studied in the synthesis of Leu-enkephaline pentapeptide carried out on a Fmoc-RinkAmide-AM-PS resin, by systematically modifying the -Gly-Gly- fragment for N-methyl or α,α-disubstituted residues and compared with the efficiency of classic aminium salt 2-(1H-benzotriazole-1-yl)-1,1,3,3-tetramethyluronium tetrafluoroborate (TBTU) under a variety of reaction conditions. In syntheses of Aib-Aib (Aib: α-aminoisobutyric acid), MeVal-MeVal, and MeLeu-MeLeu, the considerably superior performance of enkephaline analogues was obtained for DFET/NMM/BF(4) relative to TBTU, regardless of reaction conditions. Analysis of the couplings involving triazine reagent suggests that factors controlling efficiency of coupling sterically hindered substrates are the structure of the leaving group permitting formation of the cyclic intermediate or cyclic transition state and the absence of strongly solvating solvents. It has to be considered as highly probable that the absence of strongly solvating milieu favors cyclic intermediates or the cyclic transition state. Arrangement of both components into the cyclic intermediate or cyclic transition state by accumulation of the geminal (vicinal) substituents effect (known as the Thorpe-Ingold effect) would compensate retardation of the coupling process caused by steric hindrance.
2. Tetraphenylphosphonium Tetrafluoroborate/1,1,1,3,3,3-Hexafluoroisopropanol (Ph4PBF4/HFIP) Effecting Epoxide-Initiated Cation-Olefin Polycyclizations
Yan Tian, Xin Xu, Lin Zhang, Jin Qu Org Lett. 2016 Jan 15;18(2):268-71. doi: 10.1021/acs.orglett.5b03438. Epub 2016 Jan 7.
The use of an excess amount of tetraphenylphosphonium tetrafluoroborate in 1,1,1,3,3,3-hexafluoroisopropanol, which can stabilize the intermediate cation in the reaction, efficiently promoted epoxide-initiated cation-olefin polycyclization reactions with broad functional group tolerance and water and oxygen tolerance.
3. Novel three-dimensional coordination polymer of 2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethanoic acid with silver(I) tetra-fluoro-borate
Antal Udvardy, Ágnes Kathó, Gábor Papp, Ferenc Joó, Gyula Tamás Gál Acta Crystallogr E Crystallogr Commun. 2022 Feb 1;78(Pt 3):251-254. doi: 10.1107/S2056989022000767.
An AgI-based coordination polymer (CP), namely, poly[[[μ3-2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethano-ate-κ4 N:N':O,O']silver(I)] tetra-fluoro-borate], {[Ag(C9H16N3O2P)]BF4} n , was synthesized in an aqueous solution of zwitterionic 2-(1,3,5-tri-aza-7-phospho-niatri-cyclo-[3.3.1.13,7]decan-7-yl)ethan-o-ate (L) and AgBF4 with exclusion of light at room temperature. The colourless and light-insensitive CP crystallized in the monoclinic space group Cc. The asymmetric unit consists of an AgI cation, the zwitterionic L ligand and a BF4 - counter-ion. Each AgI ion is coordinated by two carboxyl-ate oxygen atoms in a chelating coordination mode, as well as one of the nitro-gen atoms of two neighbouring L ligands. The crystal structure of the CP was classified as a unique three-dimensional arrangement. The CP was also characterized in aqueous solutions by multinuclear NMR and HRMS spectroscopies and elemental analysis.
