A novel bifunctional catalyst for alkene isomerization : development, scope and limitations, and applications in organic transformations
- Author(s): Larsen, Casey Renee;
- et al.
Transition metal catalyzed alkene isomerization is a simple concept involving the atom ecomonical migration of carbon-carbon double bonds, however challenges to be met include achieving high positional and stereochemical selectivity, substrate generality, and simplicity of catalyst use. Alkene isomerization is an important technology in industry that contributes to an array of applications, including the SHOP process, DuPont's adiponitrile process, Takasago synthesis of (-)-menthol, and for the synthesis of fragrances, to name a few. This thesis describes the successful discovery and development of a novel bifunctional catalyst for alkene isomerization which has circumvented many of the general obstacles mentioned above. Notable and attractive features of the ruthenium catalyst include the following: the ability to isomerize a variety of heterofunctionalized alkenes, efficient activity under mild conditions, low loading of catalyst (even as low as 0.01-0.05 mol%), and formation of exclusively (E)-isomer products of high purity. Isomerization over as many as thirty bonds was seen, leading to the term "alkene zipper" catalyst. Kinetic studies show that our catalyst migrates double bonds over 3.5 million times faster than it performs E-to-Z- geometrical isomerism. Isomerization of neat substrate has also been demonstrated , in addition to the near quantitative isolation of pure (E)-product on a multigram scale. A second area developed herein is sequential methathesis - isomerization of alkenes, by which differentially functionalized long carbon chains can be constructed in two steps. Chains with two combinations of end groups could be made, either alcohol and aldehyde, or aliphatic ether and enol ether. Preliminary studies show that from the latter, additional end groups could be created