Poly(ε-caprolactones) Initiated by Chiral Compounds: A New Protocol to Support Organocatalysts

This work investigates the support of organocatalysts in polyesters, a class of polymers seldom used for this purpose. The proposal is to use the hydroxyl groups present in the structure of the chosen chiral compounds to promote the polymerization of ε-caprolactone, generating the support and anchoring the organocatalyst in a single step. A very simple method, with acid catalysis, was employed, that showed versatility in generating supported catalysts with different structures and functional groups and modulating the mass of the materials to generate specific solubility characteristics. In this way, the catalysts can be solubilized in some organic solvents, such as dichloromethane, but at the end of the reaction, they can be recovered in a heterogeneous way, through precipitation in more apolar solvents. The materials were applied as organocatalysts on an aldol addition test reaction and the product could be obtained in excellent yields and good stereoselectivity. The polymer did not show signs of degradation after the reaction, proving to be robust and suitable for use in catalysis; however, a recycling process appears to be necessary for its reuse.

SuFEx-Click Approach for the Synthesis of Soluble Polymer-Bound MacMillan Catalysts for the Asymmetric Diels–Alder Reaction

Novel polymeric MacMillan catalysts were prepared from modified chiral imidazolidin-4-one monomers via sulfur(VI) fluoride exchange chemistry. The resulting polysulfates containing chiral imidazolidin-4-one units could be employed as polymeric organocatalysts for the asymmetric Diels–Alder reaction. With the use of these polysulfate catalysts, sufficient catalytic activity and enantioselectivity were obtained, which were similar to those obtained by monomeric catalysts in a homogeneous catalytic reaction. In addition, the polysulfate catalysts could be recovered and reused five times without a considerable loss of activity and selectivity.

Hydrocarbon Soluble Recyclable Silylation Reagents and Purification Auxiliaries

Procedures using heptane-phase-selectively soluble octadecyldimethylsilyl groups to facilitate separations and silyl reagent regeneration are described. These results show that alcohols and alkynes protected by these groups are phase-selectively soluble in hydrocarbon solvents. In a thermomorphic cyclohexane/DMF system, >96% of the silylated alcohols are in the cyclohexane phase, allowing these compounds to be purified by a simple liquid/liquid extraction. Applications of these silylating agents in a Grignard synthesis and Sonogashira reaction are described.

Soluble Polymers as Tools in Catalysis

Examples where soluble polymers have been used in homogeneous catalysis were first noted 50 years ago, but this role for soluble polymers remained relatively unexplored until the 1990s. Since then, the use of new polymers, new developments in polymer synthesis, new separation strategies, and the imaginative ways soluble polymers' structure and physical properties can be used to influence a covalent or ligated catalyst have led to increasing interest in soluble polymers as tools in catalysis.