Mild Functionalization of Tetraoxane Derivatives via Olefin Metathesis: Compatibility of Ruthenium Alkylidene Catalysts with Peroxides

Nitro and Other Electron Withdrawing Group Activated Ruthenium Catalysts for Olefin Metathesis Reactions

Advanced applications of the Nobel Prize winning olefin metathesis reaction require user-friendly and highly universal catalysts. From many successful metathesis catalysts, which belong to the two distinct classes of Schrock and Grubbs-type catalysts, the subclass of chelating-benzylidene ruthenium complexes (so-called Hoveyda-Grubbs catalysts) additionally activated by electron-withdrawing groups (EWGs) provides a highly tunable platform. In the Review, the origin of the EWG-activation concept and selected applications of the resulting catalysts in target-oriented synthesis, medicinal chemistry, as well as in the preparation of fine-chemicals and in materials chemistry is discussed. Based on the examples, some suggestions for end-users regarding minimization of catalyst loading, selectivity control, and general optimization of the olefin metathesis reaction are provided.

4-Methyltetrahydropyran as a Convenient Alternative Solvent for Olefin Metathesis Reaction: Model Studies and Medicinal Chemistry Applications

A number of metathesis reactions were successfully conducted in 4-methyltetrahydropyran, including both standard model dienes, as well as more complex substrates, such as analogues of biologically active compounds and active pharmaceutical ingredients. To place this solvent in a context of pharmaceutical R + D, larger-scale syntheses of SUAM 1221, a prolyl endopeptidase inhibitor with potential application in Alzheimer disease treatment, and a derivative of sildenafil, an analogue of the popular Viagra drug, were executed. In the latter case, despite all the setup being made in air, the metathesis reaction at a 33 g scale proceeded very well with relatively low catalyst loading and without need of aqueous workup or column chromatography.

Sterically Tuned N-Heterocyclic Carbene Ligands for the Efficient Formation of Hindered Products in Ru-Catalyzed Olefin Metathesis

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.

Oxidative radical addition–chlorination of alkenes to access 1,1-dichloroalkanes from simple reagents

This protocol provides a facile regioselective method for the synthesis of 1,1-dichloroalkanes from terminal alkenes using simple chloro reagents.

ATRA-like alkylation–peroxidation of alkenes with trichloromethyl derivatives by the combination of tBuOOH and NEt3

This protocol provides a unique and innovative approach to the construction of α-tert-butylperoxy-β-dichloromethyl alkanes, employing CHCl₃ as an alkylating reagent to provide a –CHCl₂ group, and TBHP as an oxidant to provide an α-^tBuOO group.

Difunctionalization of alkenes with iodine and tert-butyl hydroperoxide (TBHP) at room temperature for the synthesis of 1-(tert-butylperoxy)-2-iodoethanes

We developed a direct vicinal difunctionalization of alkenes with iodine and TBHP at room temperature. This iodination and peroxidation in a one-pot synthesis produces 1-(tert-butylperoxy)-2-iodoethanes, which are inaccessible through conventional synthetic methods. This method generates multiple radical intermediates in situ and has excellent regioselectivity, a broad substrate scope and mild conditions. The iodine and peroxide groups of 1-(tert-butylperoxy)-2-iodoethanes have several potential applications and allow further chemical modifications, enabling the preparation of synthetically valuable molecules.

Bleaching Earths as Powerful Additives for Ru-Catalyzed Self-Metathesis of Non-Refined Methyl Oleate at Pilot Scale

A practical and cost-effective ruthenium-catalyzed self-metathesis of non-refined methyl oleate (85 %) derived from very high oleic sunflower oils was demonstrated at pilot scale using a robust and kg-scale commercially available SIPr-M71 pre-catalyst. The simple addition of 1 wt % bleaching earths (Tonsil 110FF) to a thermally pretreated oil could efficiently prevent catalyst deactivation. Remarkably, without the need for filtration, the catalytic system was able to achieve a turnover number (TON) of more than 744 000 at a catalyst loading of only 1 ppm. At large scale (up to 200 kg), the equilibrium of the self-metathesis reaction was reached within 1 hour at 50 °C under neat conditions at a very low 5 ppm catalyst loading to produce the expected primary metathesis products (PMP), that is, 9-octadecene and dimethyl-9-octadecenoate, with a productive TON of 94900.