Oxazoline carboxylate

Suga et al. (208,209) reported that 5-alkoxyoxazoles react with aldehydes giving 4,5-cA-2-oxazoline-4-carboxylates stereoselectively when activated with a... 

Alkoxyoxazoles undergo Lewis acid catalyzed reaction with a variety of aldehydes to give a mixture containing frani-2-oxazoline-4-carboxylates predominately. The reader is directed to a thorough review of this chemistry recently published by Suga. ... 

Keywords aromatic aldehyde, ethyl 2-cyano-2-(l-ethoxyethylidene)amino-ethanoate, dipolar cycloaddition, microwave irradiation, 4-cyano-2-oxazoline-4-carboxylate... 

Jew and Park achieved a highly enantioselective synthesis of (2S)-a-(hydroxy-methyljglutamic acid, a potent metabotropic receptor ligand, through the Michael addition of 2-naphthalen-l-yl-2-oxazoline-4-carboxylic acid tert-butyl ester 72 to ethyl acrylate under phase-transfer conditions [38]. As shown in Scheme 5.36, the use of BEMP as a base at —60 °C with the catalysis of N-spiro chiral quaternary ammonium bromide le appeared to be essential for attaining an excellent selectivity. 

A highly enantioselective synthesis of (2S)-a-(hydroxymethyl)glutamic acid, a potent metabotropic receptor ligand, has been accomplished via the catalytic Michael addition of /-butyl 2-naphthalen-l-yl-2-oxazoline-4-carboxylate to CH2=CHC02Et, using the phosphazene base (143) and the (.S )-binaphthyl quaternary ammonium salt (144) as the chiral phase-transfer reagent in CH2CI2 at — 60 °C (<97% < < ).174... 

Fraga-Drubreuil, J. and Cherouvrier, J.R. 2000. Clean solvent-free dipolar cycloaddition reactions assisted by focused microwave irradiations for the synthesis of new ethyl 4-cyano-2-oxazoline-4-carboxylates. Green Chemistry, 2 226-29. 

Oxazoline-4-carboxylic acid, cjs-5-(hy-droxymethyl)-2-phenyl-, mutarotation of, 13 Oxidation... 

The chiral ferrocenylphosphine.gold(I)-catalyzed aldol reaction of a-alkyl a-isocya-nocarboxylates 92 with paraformaldehyde gives optically active 4-alkyl-2-oxazoline-4-carboxylates 93 with moderate to good enantioselectivity [46], The absolute configuration (S) of the product indicates that the reaction occurs selectively at the si face of the enolate as illustrated in Fig. 2. These oxazolines 93 can be converted into a-alkyl-serine derivatives 94 (Sch. 24). 

Oxazoles can react at the C-4 position with aromatic aldehyde electrophiles under Friedel-Crafts conditions when the C-5 position is substituted with an alkoxy group. This feature has been exploited in a chiral Lewis acid-catalyzed formal [3-1-2] cycloaddition of aromatic aldehydes and 2-aryl-5-methoxyoxazoles 45 to generate enantiomerically enriched 2-oxazoline-4-carboxylates 46 (Scheme 4) <2001AGE1884>. These products can serve as masked /3-hydroxy a-amino acids, which are useful synthetic intermediates and have been found in peptide-based natural... 

Ibata s group extensively investigated [3 + 2] cycloaddition reactions of 5-alkoxyoxazoles with aldehydes as a means of preparing precursors of p-hydroxy amino acids or 2-amino-l,3-diols. In particular, acid hydrolysis of cw-2-oxazoline-4-carboxylates produces the relatively inaccessible erythro-p-hydroxy amino acids. The authors studied the effects of solvent, temperature, Lewis acid, and aldehyde substituent on the product distribution and developed a synthesis of 2-oxazoline-4-carboxylates that is both cii-selective and enantioselective. 

TABLE 1.58. C/S-2-OXAZOLINE-4-CARBOXYLATES AND rRAiVS-2-OXAZOEINE-4-CARBOXYEATES EROM EEWIS ACID-CATAEYZED [3 + 2] CYCEOADDITION OE OXAZOEES AND AEDEHYDES"... 

Similarly, hard Lewis acids, including SnCL, TiCLt, and (C2H5)2A1C1, also afforded the frani-oxazoline 808 as the major product. Some selected examples of cis-2-oxazoline-4-carboxylates prepared by this method are shown in Table 1.58. 

Ethyl 5-phenyl-2-oxazoline-4-carboxylate in dry ethanol hydrogenated 3 hrs. with 10%-Pd-on-diarcoal at room temp, and atmospheric pressure ethyl N-formyl-phenylalaninate. Y 99%. F. e. s. U. Sdiollkopf and D. Hoppe, Ang. Ch. 82, 483 (1970). 

Ethyl N-formyl-y -hydroxy-a-aminocarboxylates are obtained with almost 100% yield by heating ethyl 2-oxazoline-4-carboxylates 1-6 hrs. at 100° in aq. triethylamine. E. s. D. Hoppe and U. SchSllkopf, Ang. Ch. 84, 435 (1972). 

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