https://www.selleckchem.com/products/cucurbitacin-i.html Formation of tetrasubstituted C-C double bonds via olefin metathesis is considered very challenging for classical Ru-based complexes. In the hope to improve this condition, three ruthenium olefin metathesis catalysts bearing sterically reduced N-heterocyclic carbene (NHC) ligands with xylyl "arms" were synthesized, characterized using both computational and experimental techniques, and tested in a number of challenging reactions. The catalysts are predicted to initiate much faster than the analogue with mesityl N-substituents. We also foreboded the rotation of xylyl side groups at ambient temperature and the existence of all four atropoisomers in the solution, which was in agreement with experimental data. These catalysts exhibited high activity at relatively low temperatures (45-60 °C) and at reduced catalyst loadings in various reactions of sterically hindered alkenes, including complex polyfunctional substrates of pharmaceutical interest, such as yangonin precursors, chrysantemic acid derivatives, analogues of cannabinoid agonists, α-terpineol, and finally a thermally unstable peroxide.Herein, we report the rational, computationally-guided design of an iridium(I) catalyst system capable of enabling directed hydrogen isotope exchange (HIE) with the challenging sulfone directing group. Substrate binding energy was used as a parameter to guide rational ligand design via an in silico catalyst screen, resulting in a lead series of chelated iridium(I) NHC-phosphine complexes. Subsequent preparative studies show that the optimal catalyst system displays high levels of activity in HIE, and we demonstrate the labeling of a broad scope of substituted aryl sulfones. We also show that the activity of the catalyst is maintained at low pressures of deuterium gas and apply these conditions to tritium radiolabeling, including the expedient synthesis of a tritium-labeled drug molecule.Individuality in clinical gait analysis