Glycine ester, benzophenone imine

Scheme 16.21 Enantioselective Michael additions using benzophenone imine glycine ester.

Having optimized the catalytic enantioselective phase-transfer alkylation system, the group explored the scope and limitations. A variety of electrophiles were reacted with the benzophenone imine glycine tert-butyl ester 1 catalyzed by 5 mol% of the selected chiral dimeric PTCs, benzene-linked-l,3-dimeric PTC 37, 2 -F-benzene-linked-1,3-dimeric PTC 41, and naphthalene-linked-2,7-dimeric PTC 39, at reaction temperatures of 0°C or — 20 °C (Scheme 4.8). 

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

Enantioselective Alkylation of Glycine Benzophenone Imine tert-Butyl Ester. 

Allylic alkylations using a benzophenone imine of glycine methyl ester as a prochiral nucleophile and chiral phosphine ligands on palladium produced optical yields up to 57% (equation 354).436... 

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]. 

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... 

While aromatic aldimines of amino acid esters are readily accessible from benzaldehyde or related derivatives and amino acid esters with concomitant removal of water,the corresponding ketimines require harsher reaction conditions, e.g. the benzophenone imine of glycine methyl ester is formed in boiling xylene in the presence of boron trifluoride-diethyl ether complex as a Lewis acid in 82% yield.P l These or similar reaction conditions lead also to piperazine-2,5-dione (DKP) formation therefore milder reaction conditions have been developed such as the transimination with benzophenone imine in dichloromethane, which occurs at room temperature overnight in 80-95% yield (Scheme The N -diphen-... 

In 1978, O Donnell and coworkers developed the benzophenone imines of glycine alkyl esters 4 as glycine anion equivalents, which have been found to be perfed to use in the phase-transfer catalysis [10]. An essential feature of this reaction system lies in the selective mono substitution of the starting Schiff base, the O Donnell substrate 4. This can be possible because of the significant difference in acidity of a-hydrogen between starting substrate 4 p/C,(DMSO) 18.7 (R=Et)] and a-monosubstituted produd S p/C,(DMSO) 22.8 (R=Et, E = Me), 23.2 (R=Et, E = CH2Ph)] [11]. This dramatic acidity difference makes it possible for selective formation of only monoalkylated product without concomitant production of undesired dialkylated produd or racemization. 

Required Schiff base substrates were also prepared in solvent-free ball-mill conditions by mechanochemical transimination reaction. Grinding of an equimolar amount of the methyl ester of glycine hydrochloride and benzophenone imine for 3 h exclusively produced Schiff base (Scheme 2.60). Aqueous washing eliminated ammonium chloride, and the pure product was obtained without recrystallization in nearly quantitative yield. The reaction time was reduced to 3h compared with one night for the synthesis in solution. 

More recently, catalytic asymmetric allylations of imines and imine derivatives in aqueous media have been studied. An /V-spiro C2-symmetrical chiral quaternary ammonium salt (5,5)-I-Br (,S, .S )-()-Np-NAS-Br] has been evaluated in the allylation of glycine tert-Bu ester benzophenone Schiff base [Ph2C=NCH2COOCMe3] for synthesis of both natural and unnatural a-amino acids (Eq. 11,45).76... 

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