The government has certain rights in the invention. Consequently, the development of transition metal catalyzed carbon--carbon bond formation represented a significant advance in organic synthesis. One reaction involving transition metal catalyzed carbon--carbon formation is olefin metathesis.
October 4 th First proposed by Chauvin: First Asymmetric Metathesis by Grubbs and Fujimura. Mo- and W- based Catalysts: Scope and ReactivityRu-based Catalysts: Development of Metathesis Catalysts and the Jump to Asymmetry. Anti Alkylidenes in Mo-Catalysts. Syn - isomer is more stable because of an agostic interaction between the C-H bond of the alkylidene and the metal center.
The Chemistry of Schrocks Catalyst: Catalyst is highly susceptible to intermolecular decomposition pathways. Bulky imido ligands function to limit intermolecular decomposition of the catalyst1.
Alkoxide can vary greatly but must be large and bulky enough to limit intermolecular decomposition. Electron withdrawing alkoxides also influence the alkylidene geometry. Electron withdrawing groups strengthen the pseudo-triple bond between the imido ligand and the metal center.
In turn, this hinders rotation about the alkylidene. Consequently, the anti-isomer is estimated to be times more reactive towards NBDF6 than the syn-isomer. Electron withdrawing groups including phenols slow rotation enough that syn-isomer is the only one available for reaction!
Electron rich groups alkyls speed up rotation enough to compete with polymerization, hence the anti is the reacting isomer! Alkylidene Geometry is Essential for Asymmetric Induction.
Approach from the re faceMcConville, D.
Approach from the si face1. Approach from the si faceApproach from the re faceLets imagine that in a chiral environment, attack from the front face is favoured.
Lets imagine that in a chiral environment, attack from the front face is favoured. The result would be a racemic product! Approach from the si faceApproach from the si faceApproach from the re face1.
Catalysts such as [these] could selectively polymerize or ring-close one enantiomer in a racemic mixture. Grubbs and Fu demonstrate first RCM of nitrogen containing rings using Schrocks catalyst Catalysts such as [these] could selectively polymerize or ring-close one enantiomer in a racemic mixture.
Typical Reactions of Asymmetric Metathesis. R - enantiomer favoured for 5-membered rings.Ring-closing metathesis, or RCM, is a widely used variation of olefin metathesis in organic chemistry for the synthesis of various unsaturated rings via the intramolecular metathesis of two terminal alkenes, which forms the cycloalkene as the E-or Z-isomers and volatile ethylene.
The total syntheses of (+)-mycoepoxydiene and (-)A have been completed. The present synthetic strategy features the use of one-pot ring-opening/cross metathesis (ROM/CM) followed by a ring-closing metathesis (RCM) reaction, allowing for the concise construction of the 9-oxabicyclo-nona-2,4-diene framework from a 7-oxabicyclohept ene derivative and 1,3-butadiene.
Boston College The Graduate School of Arts and Sciences Department of Chemistry DEVELOPMENT OF NEW METHODS FOR CATALYTIC ENANTIOSELECTIVE OLEFIN METATHESIS. The success of enantioselective olefin metathesis relies on the design of enantioenriched alkylidene complexes capable of transferring stereochemical information from the catalyst structure to the reactants.
Cyclometalation of the NHC ligand has proven to be a successful strategy to incorporate. Apr 07, · Keywords: olefin metathesis, vicinal diol, monosaccharides, pheromones, asymmetric ring opening/cross metathesis The formation of multiple stereocenters in a single catalytic transformation is a powerful approach to the synthesis of stereochemically complex targets.
Bidirectional cross metathesis and ring-closing metathesis/ring opening of a C 2-symmetric building block: a strategy for the synthesis of decanolide natural products.