Diamino acids are important structural motifs present in many natural products and medicinal agents, and are implicated in a variety of biological functions. 1 1,2-Diamines derived from these amino acids have also found wide application as chiral auxilaries and as ligands for asymmetric synthesis. 2 Although a number of methods for their preparation exist, catalytic enantioselective variants remain rare. 1 A direct, catalytic, enantioselective Mannich reaction between a glycine equivalent and an imine, involving the creation of a C-C bond and two stereogenic centers in a single operation, represents an attractive and atom-efficient route to these compounds (eq 1). Although a handful of syntheses corresponding to this approach has been described, all lead to the selective formation of syn-configured products. 3 In this communication we detail a new synthesis of protected R,β-diamino acids, which delivers anti-configured products in good yields and with excellent enantioselectivities.
Direct Catalytic Enantioselective Mannich Reactions: Synthesis of Protected anti-α,β-Diamino Acids. -The new enantioselective route to the target compounds (III) includes a variety of aryl-, heteroaryl-, alkenyl-, and alkyl-derived imines. The corresponding isopropyl esters [cf. (V)] allow epimerization into the syn-diastereomers. -(CUTTING, G. A.; STAINFORTH, N. E.; JOHN, M. P.; KOCIOK-KOEHN, G.; WILLIS*, M. C.; J.
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