4-Carboxy-oxazoline

Ring closure of (3-hydroxy-a-amino acids with sulfuryl chloride/triethylamine 68 is accompanied by formation of (3-chloroalanine,16 1 whereas cyclization of urethane-protected serine and threonine by the Mitsunobu reaction 54 69 70 leads to oxazoline and dehydroalanine formation as side products. 47,71 Formation of dehydroalanine can be prevented by bulky carboxy protecting groups such as tert-butyl esters. 69 ... 

Masked chiral a-hetero substituted carboxylic acid enolates have also shown utility in dia-stereoselective additions to nitroalkenes. For example, derivatives of a-hydroxycarboxylic acids, e.g. l,3-dioxolan-4-ones (187) a-amino acids, e.g. 1,3-imidazolidin-4-ones (188) and a-amino-fi-hydroxy-carboxylic acids, e.g. methyl 1,3-oxazolidin-4-carboxylates (189) and methyl l,3-oxazolin-4-carboxy-lates (190), have been employed.1S0a Further, diastereoselective additions of chiral (3-hydroxyesters (191), via the enediolates, to nitroalkenes (40) afford predominant anr/ -P-hydroxyesters (192 Scheme... 

Methylthiophene is metallated at the S-position whereas 3-methoxy-, 3-methylthio-, 3-carboxy-, and 3-bromo-thiophenes are metallated at the 2-position. 2-Substituents which have been used to direct metallation to C(3) of thiophene include oxazoline, imidazoline, secondary carboxamide, carboxylate, sulfonamide, and -aminoalkoxide. For... 

The carboxy-group has been protected in lithium aluminium hydride reductions by conversion into 2-oxazolines (639) through acid-catalysed rearrangement of the corresponding aziridine. The carboxylic acid or... 

Miyamoto, M., Naka, K., Tokumizu, M., and Saegusa, T. (1989) End capping of growing species of poly(2-oxazoline) with carboxylic acid A novel and convenient route to prepare vinyl- and carboxy-tenninated macromonomers. 

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