Chemoselective O-acylation of hydroxyamino acids and amino alcohols under acidic reaction conditions: History, scope and applications.

Amino acids, whether natural, semisynthetic or synthetic, are among the most important and useful chiral building blocks available for organic chemical synthesis. In principle, they can function as inexpensive, chiral and densely functionalized starting materials. On the other hand, the use of amino acid starting materials routinely necessitates protective group chemistry, and in reality, large-scale preparations of even the simplest side-chain derivatives of many amino acids often become annoyingly strenuous due to the necessity of employing protecting groups, on one or more of the amino acid functionalities, during the synthetic sequence.

Combined bead polymerization and Cinchona organocatalyst immobilization by thiol-ene addition.

In this work, we report an unusually concise immobilization of Cinchona organocatalysts using thiol-ene chemistry, in which catalyst immobilization and bead polymerization is combined in a single step. A solution of azo initiator, polyfunctional thiol, polyfunctional alkene and an unmodified Cinchona-derived organocatalyst in a solvent is suspended in water and copolymerized on heating by thiol-ene additions. The resultant spherical and gel-type polymer beads have been evaluated as organocatalysts in catalytic asymmetric transformations.

A general approach for preparation of polymer-supported chiral organocatalysts via acrylic copolymerization.

Polymer-supported chiral organocatalysts, as well as most other forms of immobilized catalysts, are traditionally prepared by a postmodification approach where modified catalyst precursors are anchored onto prefabricated polymer beads. Herein, we report an alternative and more scalable approach where polymer-supported chiral enamine and iminium organocatalysts are prepared in a bottom-up fashion where methacrylic functional monomers are prepared in an entirely nonchromatographic manner and subsequently copolymerized with suitable comonomers to give cross-linked polymer beads. All syntheses have been conducted on multigram scale for all intermediates and finished polymer products, and the catalysts have proven successful in reactions taking place in solvents spanning a wide range of solvent polarity.

Synthesis of acrylic polymer beads for solid-supported proline-derived organocatalysts.

A completely non-chromatographic and highly large-scale adaptable synthesis of acrylic polymer beads containing proline and prolineamides has been developed. Novel monomeric proline (meth)acrylates are prepared from hydroxyproline in only one step. Free-radical copolymerization then gives solid-supported proline organocatalysts directly in as little as two steps overall, without using any prefabricated solid supports, by using either droplet or dispersion polymerization.