Cross-metathesis of vinylsilanes with olefins in the presence of Grubbs’ catalyst

Nucleophilic Activation of Alkenyl and Aryl Boronates by a Chiral CuIF Complex: Catalytic Enantioselective Alkenylation and Arylation of Aldehydes

A new method for the catalytic enantioselective alkenylation and arylation of aldehydes involves the activation of alkenyl and aryl boronates by a catalytic amount of the Cu(I)F-DTBM-segphos complex through transmetalation, generating novel alkenyl and aryl copper species. These reagents act as the actual nucleophile. A range of aldehydes can be converted into optically active secondary allyl alcohols or diaryl methanols with excellent enantioselectivity. The appropriate choice of additives, depending on the substrate, is critical to ensure high yields of products. These additives possibly modulate the catalyst turnover step from copper alkoxide intermediates generated by the addition of organocopper reagents to aldehydes.

Synthesis of Bicyclo[3.1.0]hexanes Functionalized at the Tip of the Cyclopropane Ring. Application to the Synthesis of Carbocyclic Nucleosides

[reaction: see text] A general synthetic strategy for the preparation of functionalized bicyclo[3.1.0]hexanes is described. The new approach employs a cross metathesis step designed to functionalize the appropriate terminal olefin of the bicyclo[3.1.0]hexane precursor and a carbene-mediated intramolecular cyclopropanation reaction on the corresponding diazo intermediate. This combined methodology allowed the diastereoselective introduction of chemically diverse substituents at the tip of the cyclopropane group, except in cases where the substituents consisted of electron-withdrawing groups where a competing [3 + 2] cycloaddition predominated.

Enantioselective Alkenylation and Phenylation Catalyzed by a Chiral CuF Complex

A new method for CuF-catalyzed alkenylation and phenylation of aldehydes and an activated ketone using air- and moisture-stable alkenylsilanes and phenylsilane as a nucleophile is described. This methodology was extended to highly enantioselective catalytic alkenylation and phenylation using DTBM-SEGPHOS as a chiral ligand. Substrate generality is broad, and an alkenylsilane with a long alkyl chain and an internal alkenylsilane can be also used as a nucleophile. The key to success partly involves the accelerated regeneration of reactive alkenylcopper and phenylcopper through transmetalation from the silylated nucleophiles, and stabilization of the reactive copper reagents, both of which are effected by the diphosphine ligands.

Regio- and stereoselective hydrosilylation of terminal alkynes using Grubbs' first-generation olefin-metathesis catalyst

Grubbs' first-generation, Ru metathesis complex catalyses the hydrosilylation of terminal alkynes. The reaction exhibits an interesting selectivity profile that is dependent on the reaction concentration and more importantly on the silane employed.

Functionalization vs. degradation of 1,4-polybutadiene by ruthenium complex catalyzed reaction with vinylsilanes

Polybutadiene (I) containing 91% of 1,4-(cis-trans) units and 9% of 1,2-units in the presence of vinyltriethoxysilane (II) and ruthenium catalysts RuCl2(PPh3)3 (III), RuHCl(CO)(PPh3)3 (IV), and [RuCl2(CO)3]2 (V) at 100-130°C undergoes functionalization and (or) partial degradation as an effect of competitive silylative coupling of =C-H and cross-metathesis of I with II. Significant degradation of I occurs at lower temperatures (100-110°C) (particularly when the process is carried out in air), but exclusive functionalization of I is observed at higher temperature (120-130°C) regardless of the atmosphere (air or argon) used.Key words: functionalization, degradation, polybutadiene, ruthenium complexes.