Highly selective macrocyclic ring-closing metathesis of terminal olefins in non-chlorinated solvents at low dilution

Abstract

New ruthenium complexes featuring two unsymmetrical NHCs proved to be highly selective in macrocyclic RCM performed in green solvents at low dilution.

Design of bis-NHC Ru-complexes featuring diarylmethylene N-substituents for olefin metathesis

“…The 1 M solution of hydrogen chloride in ethanol and 0.5 M solution of KHMDS were purchased from Acros Organics with AcroSeal packaging. NMR spectra were recorded on a Bruker ARX400 spectrometer ( 1 H (400 MHz), 13 C (101 MHz), 19 F (376 MHz) and 11 B (128 MHz)) with complete proton decoupling for 13 C. Chemical shifts are reported in parts per million with the solvent resonance as the internal standard (CDCl3, 1 H: δ 7.26 ppm, 13 C: δ 77.16 ppm; DMSO, 1 H: δ 2.50 ppm, 13 C: δ 39.52 ppm). Coupling constants are reported in Hertz (Hz).…”

“…18 These catalysts were quite efficient in various metathesis transformations, notably in macrocyclic RCM of terminal dienes affording various macrocyclic odorant molecules of remarkable >99% purity. 19 In front of these results, we decided to continue the development of latent Ru-complexes by introducing novel NHC ligands. We report herein the synthesis of new ruthenium indenylidene complexes Ru-11 containing two symmetrical NHCs featuring diarylmethylene fragments.…”

“…More recently, we synthesised two new latent complexes Ru-9 and Ru-10 bearing two unsymmetrical unsaturated N-cycloalkyl-NHCs that were activated by anhydrous HCl 18. These catalysts were quite efficient in various metathesis transformations, notably in macrocyclic RCM of terminal dienes affording various macrocyclic odorant molecules of remarkable >99% purity 19. In front of these results, we decided to continue the development of latent Ru-complexes by introducing novel NHC ligands.…”

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

“…Ring-closing metathesis (RCM) allows for the easily formation of medium-large size rings, which would be less practicable using alternative strategies. Several catalysts have been developed for this task, achieving high activities (with TONs up to 315,000) and selectivities [582][583][584][585].…”

Continuous Flow Z‐Stereoselective Olefin Metathesis: Development and Applications in the Synthesis of Pheromones and Macrocyclic Odorant Molecules**

“…As numerous highly valuable molecules feature a Z-alkene moiety, special attention has recently been focused on the development of a new class of Ru-based complexes to enable high selectively towards Z-olefins (Figure 1). 5 Cyclometalated Ru-catalyst Ru-1 (Grubbs) 6 and monothiolate Ru-catalyst Ru-2 (Jensen) 7 have proved to be highly Z-stereoselective in cross-metathesis (CM) of terminal olefins (up to >99:1) while stereoretentive dithiolate catalyst Ru-3 (Hoveyda) 8 efficiently promoted the transformation of Z-olefins into corresponding Z-products by retaining the stereochemical information (up to >99:1). Recently, we described the synthesis of a cost-effective Z-selective cyclometalated Ru-catalyst Ru-4 9 featuring an unsymmetrical unsaturated NHC (U2-NHC) ligand accessible through a multicomponent process.…”