Recent applications of olefin metathesis to combinatorial chemistry

Olefin Cross-Metathesis in Polymer and Polysaccharide Chemistry: A Review

Olefin cross-metathesis, a ruthenium-catalyzed carbon-carbon double bond transformation that features high selectivity, reactivity, and tolerance of various functional groups, has been extensively applied in organic synthesis and polymer chemistry. Herein, we review strategies for performing selective cross-metathesis and its applications in polymer and polysaccharide chemistry, including constructing complex polymer architectures, attaching pendant groups to polymer backbones and surfaces, and modifying polysaccharide derivatives.

Imparting functional variety to cellulose ethers via olefin cross-metathesis

Olefin cross-metathesis (CM) was applied to impart functional variety to a series of cellulose ether derivatives.

An aldol-based build/couple/pair strategy for the synthesis of medium- and large-sized rings: discovery of macrocyclic histone deacetylase inhibitors

An aldol-based build/couple/pair (B/C/P) strategy was applied to generate a collection of stereochemically and skeletally diverse small molecules. In the build phase, a series of asymmetric syn- and anti-aldol reactions were performed to produce four stereoisomers of a Boc-protected γ-amino acid. In addition, both stereoisomers of O-PMB-protected alaninol were generated to provide a chiral amine coupling partner. In the couple step, eight stereoisomeric amides were synthesized by coupling the chiral acid and amine building blocks. The amides were subsequently reduced to generate the corresponding secondary amines. In the pair phase, three different reactions were employed to enable intramolecular ring-forming processes: nucleophilic aromatic substitution (S(N)Ar), Huisgen [3+2] cycloaddition, and ring-closing metathesis (RCM). Despite some stereochemical dependencies, the ring-forming reactions were optimized to proceed with good to excellent yields, providing a variety of skeletons ranging in size from 8- to 14-membered rings. Scaffolds resulting from the RCM pairing reaction were diversified on the solid phase to yield a 14 400-membered library of macrolactams. Screening of this library led to the discovery of a novel class of histone deacetylase inhibitors, which display mixed enzyme inhibition, and led to increased levels of acetylation in a primary mouse neuron culture. The development of stereo-structure/activity relationships was made possible by screening all 16 stereoisomers of the macrolactams produced through the aldol-based B/C/P strategy.

An expeditious synthesis of 4-hydroxy-2E-nonenal (4-HNE), its dimethyl acetal and of related compounds

The facile one step synthesis of 4-hydroxy-2E-nonenal and its dimethyl acetal via a cross-metathesis reaction between commercially available octen-3-ol and acrolein or its dimethyl acetal is reported. The method was extended to the synthesis of C6 and C12 4-hydroxy-2E-enals, their dimethyl acetal and of the 4-hydroxy-2E-nonenoic acid (4-HNA).

Synthesis of 3-(Aryl)alkenyl-β-lactams by an Efficient Application of Olefin Cross-Metathesis on Solid Support

[reaction: see text] An efficient cross-metathesis on solid support for the synthesis of beta-lactam analogues of cholesterol absorption inhibitors is described. The applied strategy allows the introduction of diversity in positions 3 and 4 of the beta-lactam ring with excellent 3,4-trans selectivity and complete E selectivity at the C-3 side chain.

From solution-phase to solid-phase enyne metathesis: crossover in the relative performance of two commonly used ruthenium pre-catalysts

A crossover in the ability of two distinct ruthenium-based metathesis pre-catalysts to effect the synthesis of dialkenylboronic esters in solution and on the solid-phase was observed. Specifically, while the Grubbs 2nd generation pre-catalyst 3 affords a greater degree of conversion to product than the Hoveyda-Grubbs pre-catalyst 2 in a solution-phase enyne-metathesis reaction, this trend is reversed in the solid-phase variant. Systematic investigation showed this trend to be general, regardless of variations in the homoallylic alcohol and alkynylboronic ester components of the reaction, as well as in the type of solid support employed. Experiments to determine a mechanistic hypothesis for this trend highlighted the significance of the ruthenium remaining bound to the substrate after metathetic rearrangement and found the presence of phosphine ligand to be detrimental to the success of the solid-phase reaction. Therefore, these results suggest an expanded role for phosphine-free pre-catalysts, such as 2, in challenging solid-phase metathesis reactions.

Photocurable hard and porous biomaterials from ROMP precursors cross-linked with diyl radicals

A combination of (ROMP) ring-opening metathesis polymerization and diradical (diyl) cross-linking provides a new access to hard biomaterials and potential artificial bone replacements. ROMP was used to construct soft and pliable linear polymers bearing photolabile diazene functions. After treatment with light, a nitrogen aerosol is released throughout the polymer to create desirable porosity, cross-linking, and hardening in a single step. Nonpolymeric mechanistic work supporting these studies was also examined.