Imidates, oxazoline synthesis

The first synthesis and use of a chiral oxazoline was reported by Meyers in 1974. The chiral oxazoline 1 was prepared in two steps by condensation of (-i-)-l-phenyl-2-amino-1,3-propanediol (6) with the ethyl imidate of propionitrile followed by 0-methylation of the resulting alcohol 7 with NaH/Mel. Meyers demonstrated chiral oxazoline 1 could be... 

An efficient and practical two-step [4-1-1] oxazole synthesis utilizes the condensation of serine methyl ester with ethyl imidate 193 to give an intermediate oxazoline 194. Treatment of 194 under basic conditions brings about elimination of hydrogen chloride to give oxazole 195 in high yield (Scheme 54) <20010PD37>. 

A recent synthesis of (+)-z5o-6-cassine makes use of enantioselective Overman rearrangement of imidate 74. Treatment of 74 with chiral cobalt oxazoline palladacycle (5)-COP-Cl vide supra) in dichloromethane gives rise to the iV-trichloroacetyl derivative 75 in good yield. This asymmetric reaction installs the absolute stereochemistry of C-6 in (+)-fso-6-cassine. ... 

Substituted-2-oxazoline-5-ones are extremely useful for the synthesis of a-aminoacids and peptides. A report on their formation using a water-soluble carbodi-imide for the dehydration-cyclization step has now appeared (Scheme 49). Previous methods for cyclization of hippuric acid (356) and its derivatives include use of AC2O, PX3, and DCC. The water-soluble carbodi-imide method gave a good yield and made work-up simpler. 

Sibi et al. demonstrated for the first time that intermolecular radical addition to a,P-disubstituted substrates (12) followed by hydrogen atom transfer proceeded with high diastereo- and enantioselectivities (Scheme 4.6) [4]. In particular, a chiral bis(oxazoline)s-Mgl2 catalytic system was applied to the enantioselective and highly diastereoselective antijsyn = 99/1) synthesis of anti-aldol-type adducts (13). This is noteworthy because there have been few examples of highly selective methods for preparing anti aldol despite the array of solutions for the synthesis of syn aldol. The key to increasing the reactivity for a,P-disubstituted substrate (12) was N-H imide templates that relieve problems, and the promotion of Lewis acid catalysis via... 

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