Glycinate benzophenone imines

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. 

A Enantioselective Alkylation of Glycine Benzophenone Imine tert-Butyl... 

Preparation of 0-Allyl-N-(9)-anthracenylmethylcinchonidinium Bromide as a Phase Transfer Catalyst for the Enantioselective Alkylation of Glycine Benzophenone Imine tert-Butyl Ester. 

PREPARATION OF 0-ALLYL-N-(9-ANTHRACENYLMETHYL) CINCHONIDINIUM BROMIDE AS A PHASE TRANSFER CATALYST FOR THE ENANTIOSELECTIVE ALKYLATION OF GLYCINE BENZOPHENONE IMINE tert-BUTYL ESTER (4S)-2-(BENZHYDRYLIDENAMINO)PENTANEDIOIC ACID, 1-tert-BUTYL ESTER-5-METHYL ESTER... 

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. 

Scheme 5.5 Enantioselective 103a-catalyzed Michael reaction of tert-butyl glycinate benzophenone imine with several enones under PTC conditions.

Scheme 5.8 Enantioselective Michael reaction of glycinate benzophenone imines with several enones in solid phase and in solution.

---