Expanding the Applications of Transition Metal Alkylidenes and Alkylidynes to Organic Synthesis

Citation

Kirkland, Thomas Andrew (2000) Expanding the Applications of Transition Metal Alkylidenes and Alkylidynes to Organic Synthesis. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/w770-7r65. https://resolver.caltech.edu/CaltechTHESIS:08292024-181421142

Abstract

The application of olefin and acetylene metathesis to organic synthesis has increased greatly since its introduction. The research in this thesis describes the Ring-Closing Metathesis (RCM) of substituted olefins and enynes, the metathesis of internal acyclic olefins and the conversion of acid chlorides to acetylenes with tungsten alkylidynes.

In Chapter 1, the activity of ruthenium alkylidenes and molybdenum alkylidenes for the RCM of dienes containing gem-disubstituted olefins was investigated. Dienes with sterically-demanding and/or electron-withdrawing substituents were cyclized successfully with only the molybdenum alkylidene. Dienes with allylic functional groups yielded functionalized cyclic olefins when treated with either alkylidene.

In Chapter 2 the cyclization of enyne and endiyne substrates using ruthenium alkylidenes was discussed. The effects of ring size and methyl substitution on the conversion were determined. A mechanism in which the alkylidene reacts with the olefin first, followed by an intramolecular reaction with the acetylene on an enyne substrate is described.

The RCM of acyclic dienes containing vicinally substituted olefins was described in Chapter 3. Water-soluble ruthenium alkylidenes did not cyclize α,ω-dienes due to the instability of the resulting methylidene. The incorporation of a phenyl substituent resulted in nearly quantitative cyclization. RCM of a water-soluble diene has been achieved in aqueous solution using this methodology. This methodology has also been successfully applied to increase RCM yields in organic solvents.

The stereoselectivity of metathesis of acyclic olefins was investigated for several ruthenium alkylidenes in Chapter 4. This was primarily done using cis-2-pentene metathesis. Data from cis-2-pentene metathesis was also used to determine relative metathesis rates for various alkylidenes and reaction conditions. An alkylidene bearing tricyclopentyl phosphines (13) was significantly more cis selective than one with tricyclohexyl phosphines (8). Alkylidene 8 was moderately cis selective for cis-2-pentene metathesis and slightly cis selective for trans-2-pentene metathesis.

An investigation into the conversion of acid chlorides to substituted acetylenes using tungsten alkylidynes is discussed in Chapter 5. A new route to DIPP tungsten alkylidynes is described. Several aromatic acid chlorides were converted into acetylenes using these alkylidynes in good yields. Finally, attempts at the synthesis of W₂(DIPP)₆ are described.

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