ABSTRACT
An efficient method for enantioselective synthesis of highly functionalized pyrans (up to 98% ee) through Ru-catalyzed asymmetric ring-opening metathesis/cross-metathesis is described. Reactions are promoted by a recyclable chiral Ru-chloride or a new chiral Ru-iodide complex; the latter catalyst is less efficient but gives rise to significantly higher levels of enantioselectivity. Catalytic reactions can be performed in undistilled solvent and with a wide range of substrates, including those that contain secondary and tertiary alcohols. Representative regioselective functionalizations that highlight the utility of the catalytic method are also presented.
ABSTRACT
The discovery and development of a new class of Ru-based catalysts for olefin metathesis is described. These catalysts, particularly those that do not bear a phosphine ligand, have been demonstrated to promote unique levels of reactivity in a variety of olefin metathesis reactions. The design and development of supported and chiral optically pure variants of this class of Ru catalysts for use in enantioselective metathesis are discussed as well. All catalysts are air stable, reusable, and can be employed with unpurified solvents.
ABSTRACT
Design, synthesis, characterization, and catalytic activity of six enantiomerically pure Ru-based metathesis catalysts are disclosed (3a-3f). The new chiral catalysts were prepared through steric and electronic alterations of the parent catalyst system (3). The present studies indicate that the effect of structural modifications of chiral complex 3 does not always correspond to those of the related achiral complexes. The present findings illustrate that modified Ru complexes (3e and 3f) deliver reactivity levels that are more than 2 orders of magnitude higher than 3. Reactivity and physical data are provided that shed light on the origin of activity differences. Some members of the new generation of chiral Ru catalysts promote asymmetric ring-opening (AROM) and ring-closing (ARCM) metatheses that cannot be effected by the first generation chiral catalyst (3).
ABSTRACT
The synthesis and structure of a new chiral bidentate imidazolinylidene ligand and a derived chiral Ru-based carbene are disclosed. The Ru complex is stereogenic at the metal center; it can be prepared in >98% diastereoselectivity and purified by silica gel chromatography with undistilled solvents. The air-stable Ru complex efficiently catalyzes ring-closing and ring-opening metathesis and is recyclable. The chiral complex is highly effective (0.5-10 mol % loading) in promoting enantioselective ring-opening/cross metathesis reactions (up to >98% ee). These enantioselective transformations can be effected in air, with unpurified solvent and with substrates that would only polymerize with Mo-based catalysts.
ABSTRACT
Glass-bound Ru-based catalysts! Ru-containing glass pellets efficiently promote olefin metathesis reactions and are easily employed in syntheses of compound libraries. These robust catalysts are active in air and commercially available solvents, can be recycled up to 16 times, and removed from reaction mixtures with a simple pair of tweezers (minimal solvent waste).