Organocatalysis amino acids-derived bases

Recently, a dual organocatalysis approach, namely, the combination of the achiral nucleophilic Lewis base catalyst DMAP (23) and the chiral anion-binding thiourea catalyst 27, was applied to the Steglich rearrangement to provide a,a-disubstituted amino acid derivatives 24 in a highly enantioselective fashion (Scheme 43.5) [14]. Notably, replacement of the nucleophilic codiamino acid derivatives with excellent enantiomeric excesses (88-93% ee). 

A pioneer in the field of the asymmetrie (thio)urea organocatalysis was Eric Jacohsen, who first reported a chiral (polymer-hound) Schiff base thiourea derivative for asymmetric Strecker reactions optimised from parallel synthetic libraries/ These catalysts can be used either in solution or immobilised to a polystyrene resin, with the latter retaining efficiency, after repeated recycling/ The key factors responsible for high enantioselectivities were the presence of bullqr substituents at both the amino acid position and at the 3-position of the aromatic ring (Scheme 19.3). 

Although boron is a metalloid, one can nonetheless include boron-derived compounds in a book on organocatalysis as not being transition metal containing catalysts Planar chiral boronic acids have been employed as amide couphng catalysts, actually as bifunctional Lewis acid/base activators. Whiting s [51] group reported the preparation [52] of two amino-boronic ferrocenes (see Scheme 8.17). Their use... 

---