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

Abstract

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.

Organocatalysis in the Chemical Transformations

“…Thus, this Special Issue is dedicated to the field of organocatalysis and the latest developments regarding the optimization of the organocatalysts using distinct methodologies, with the commitment of meeting the environmental requirements, highlighting the importance of green solvents and catalyst recycling, as well as the need to correlate the waste produced in relation to the useful product for upscaling purposes [2][3][4][5][6][7][8], as briefly described in the following paragraphs.…”

“…According to the authors, products could be recovered with good efficiency via supercritical CO 2 extraction. Likewise, Jacoby et al [3] demonstrated the feasibility of recovering products and catalysts through the development of novel polyestersupported catalysts (PCL) prepared from poly(ε-caprolactones), modulating the molecular weights in order to control the catalyst/polymer weight ratio, ensuring homogeneous catalysis, while allowing the catalysts to recover through CO 2 supercritical extraction. In terms of catalyst performance, the presence of amide groups decorating the catalysts' structures was more effective than the presence of their ester group counterparts toward the aldol product, achieving a higher degree of steroselectivity.…”