Polymer-Supported Glyoxylate and α-Imino Acetates. Versatile Reagents for the Synthesis of α-Hydroxycarboxylic Acid and α-Amino Acid Libraries

Abstract
Polymer-supported glyoxylate·monohydrate (3) and α-imino acetates (7) have been readily prepared from chloromethylated resin via two or three steps. The ene reactions of 3 with alkenes were successfully performed in the presence of Yb(OTf)3 (50 mol %) to afford, after cleavage from the polymer support, the corresponding α-hydroxycarboxylic acid esters in good yields. The reactions of 7 with silyl enolates, Danishefsky's diene, and alkenes also proceeded smoothly in the presence of Sc(OTf)3 (20 mol %) to give the corresponding α-amino acid, pyridone, and tetrahydroquinoline derivatives, respectively, in good yields.