Ethyl glycinate benzophenone imine

Ma and co-workers extended use of chiral guanidine catalysts to the addition of glycine derivatives to acrylates [121], Addition products were achieved in high yield with modest enantioselectivity (Scheme 67). The ferf-butyl glycinate benzophenone imines generally provided better enantiomeric ratios than the ethyl glycinate benzophenone imines. Based on this observation, the authors hypothesized that an imine-catalyst complex determines the stereochemical outcome of the product. 

Scheme 5.4 Enantioselective Michael reaction of ethyl glycinate benzophenone imine with several enones using chiral crown ethers as catalysts.

Another relevant pioneering report in this context was carried out by Corey, using cinchona-based chiral ammonium salt 103a as catalyst (Scheme 5.5). In this case, the conjugate addition of tert-butyl glycinate benzophenone imine to cyclohexanone and ethyl vinyl ketone was found to proceed with excellent yields and enantioselectivities and, in the cyclohexanone case, also with almost complete diastereoselectivity. Cesium hydroxide was selected for this particular reaction as the most appropriate base to generate the reactive enolate species. 

Protected glycine derivatives have been used as the nucleophilic partner in enantioselective syntheses of amino acid derivatives by chiral PTC (Scheme 10.9). Loupy and co-workers have reported the addition of diethyl acetylaminomalonate to chalcone without solvent with enan-tioselectivity up to 82% ee [44]. The recent report from the Corey group, with catalyst 8a used in conjunction with the benzophenone imine of glycine t-butyl ester 35, discussed earlier, results in highly enantioselective reactions (91-99% ee) with various Michael acceptors (2-cyclo-hexenone, methyl acrylate, and ethyl vinyl ketone) to yield products 71-73 [21], Other Michael reactions resulting in amino acid products are noted [45]. 

Cyclopropylideneethanol carbonate (Scheme 22) reacts with many nitrogen and stabilized carbon nucleophiles, including benzophenone imine of ethyl glycinate. ... 

The Schiff s base derived from ethyl glycinate and benzophenone has been alkylated under both anhydrous and phase transfer conditions yielding, after hydrolysis, a-amino acids. Under phase transfer conditions, alanine, a-aminobutyric acid, valine, leucine and phenylalanine were prepared in 91%, 86%, 61%, and 55% yields, based on starting imine. 

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