Trans-2-oxazoline-4-carboxylates

TABLE 1.58 C/S-2-OXAZOLINE-4-CARBOXYLATES AND TRANS-2-OXAZOLINE-4-CARBOXYLATES FROM LEWIS ACID-CATALYZED [3 + 2] CYCLOADDmON OF... 

N-Acylaziridine-2-carboxylates readily rearrange to oxazolines under thennal, acidic, or nucleophilic conditions [91, 123-127]. Treatment of trans-aziridine-2-car-boxylate 176 (Scheme 3.63) with Nal in acetonitrile, for example, resulted in ring-expansion product 177 through the so-called Heine reaction. The reaction involves initial opening of the aziridine ring by iodide and subsequent oxazoline ring-closure by Sn2 displacement of the resultant iodide intermediate [127]. 

The copper(l) triflate complex of 1 has been evaluated in the asymmetric cyclopropanation of styrene with ethyl diazoacetate (eq 3). The trans- and cis -2-phenylcyclopropane carboxylates were isolated in 88% yield as a 70 30 ratio of diastereomers in 43% and 44% enantioselectivity. These enantioselectivities are not as high as observed with other bis(oxazoline) ligands. 

Lee S-H, Yoon J, Nakamura K, Lee Y-S (2000) Efficient Syntheses and Ring-Opening Reactions of trans- and c/5-Oxazoline-5-carboxylates. Org Lett 2 1243... 

Fig. 8. Alternative catalytic nucleophiles, (a) Tyrosine functions as the catalytic nucleophile in Clan GH-E sialidases and trans-silalidases, with the assistance of a proximal carboxylate amino acid side chain, (b) Anchimeric assistance in hexosaminidases involving reaction of the A -acetyl group of the substrate with the anomeric carbon to form an oxazoline intermediate in the enzyme active site, (c) Sugar thiazolines are noncleavable S-linked inhibitors of hexosaminidases that use an oxazoline intermediate. Enz5mie selectivity can be further tuned by varying i . ...

A pseudo-C(2) symmetric trans-diphenyl oxazoline group has been reported to act as a chiral auxiliary in the 8k, 6k tandem electrocyclization of a substituted tetraene 1-carboxylic acid in a process where both s-cis and s-trans conformations favour the transition states with the same helical twist (Scheme 29) ... 

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