Amino acids with electron-donating groups

Using a ball milling technique, the desired aldols 58a can be synthesized in a proline-catalyzed reaction (10 mol% catalyst loading) with no solvent added [77]. In addition to proline, a variety of primary amino acids catalyze this reaction, indicating that the five-membered ring is not crucial to catalytic efficacy [62, 78, 79, 80]. The results are very impressive for aldehyde 2a but less so for benzaldehydes with electron-donating groups. 

The Alper group [163] reported on a highly efficient double carbohydroamination for the preparation of a-amino carboxylic acid amides 6/1-345, starting from aryl iodides and a primary amine 6/1-344, in usually high yield (Scheme 6/1.88) both, aryl iodides with electron-donating and electron-withdrawing groups can be used. 

With the optimized conditions in hand we explored the scope of the Brpnsted acid catalyzed hydrocyanation of various imines (Table 8). In general, high enantioselectivities and good isolated yields of several aromatic and heteroaromatic, Af-benzyl- and /V-paramethoxy-benzyl protected amino nitriles, bearing either electron-withdrawing or electron-donating groups are obtained. These products are important precursors for the synthesis of amino acids and diamines. Hence, in order... 

The effect of electronic configuration of the acceptor is particularly apparent in the contrast of Ser/Thr and Tyr hydroxyl groups the phenolic hydroxyl of tyrosine has a preference for near-plane position for donors and/or acceptors, as its sp hybridization leaves the lone pair electrons in the plane of the ring [15, 16], whereas serine and threonine hydroxyls have sp hybridization with two acceptor and one donor position at 120° spacing (the donating proton is usually trans to the carbon three covalent bonds away). The observed spatial distributions for the principal amino acid donor and acceptor groups are illustrated schematically in Fig. 6.1. 

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