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20.2.7.1.3.5.1 Method 1: Addition of Grignard Reagents to Chiral Dehydromorpholinones

DOI: 10.1055/sos-SD-020-00343

Wolkenberg, S. E.; Garbaccio, R. M.Science of Synthesis, (200720462.

Dehydromorpholinones 245 typically undergo Grignard addition to the ester moiety; however, in the presence of a Lewis acid, regiospecific addition occurs to the imine (Scheme 65). This observation allows for the synthesis of α-alkyl-α-amino acids[‌199‌] from this ubiquitous template. Following precomplexation with the boron trifluoridediethyl ether complex, a range of Grignard reagents can be added anti to the phenyl group to produce a single diastereomer of 246. Cleavage of the morpholinone is achieved by hydrogenolysis to produce disubstituted amino acids 247. The scope of the transformation is demonstrated for methyl-substituted morpholinones; however, other aliphatic templates are successfully made.

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