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diastereoselective synthesis of α-methylpyroglutamates from α,β-didehydro α-amino acids

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2003 Amino acids Amino acids U 0400 Diastereoselective Synthesis of α-Methylpyroglutamates from α,β-Didehydro α-Amino Acids. — The route to the title compounds involves chemoselective addition of methylmagnesium bromide to the C=N bond of starting pyridazones in the presence of Yb(OTf) 3 , ring contraction of resulting perhydropyridazones under treatment with LiN(Tms) 2 , and reduction of the N-benzylideneaminopyrrolidines with Raney nickel. In the appropriate cases, the perhydropyridazones are obtained as single diastereomers. In contrast, the ring contraction of perhydropyridazones (XIII) and (XVII), derived from cis and trans compounds (XII) and (XVI), gives the same diastereomer (XIV) indicating an epimerization at C-5. — (ALVAREZ-IBARRA*, C.; CSAKY, A. G.; GOMEZ DE LA OLIVA, C.; Eur. J. Org. Chem. 2002, 24, 4190-4194; Dep. Quim. Org., Fac. Farm., Univ. Complutense, E-28040 Madrid, Spain; Eng.) — Klein 15- 194

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Page 1: Diastereoselective Synthesis of α-Methylpyroglutamates from α,β-Didehydro α-Amino Acids

2003 Amino acids

Amino acidsU 0400 Diastereoselective Synthesis of α-Methylpyroglutamates from α,β-Didehydro

α-Amino Acids. — The route to the title compounds involves chemoselective addition of methylmagnesium bromide to the C=N bond of starting pyridazones in the presence of Yb(OTf)3, ring contraction of resulting perhydropyridazones under treatment with LiN(Tms)2, and reduction of the N-benzylideneaminopyrrolidines with Raney nickel. In the appropriate cases, the perhydropyridazones are obtained as single diastereomers. In contrast, the ring contraction of perhydropyridazones (XIII) and (XVII), derived from cis and trans compounds (XII) and (XVI), gives the same diastereomer (XIV)indicating an epimerization at C-5. — (ALVAREZ-IBARRA*, C.; CSAKY, A. G.; GOMEZ DE LA OLIVA, C.; Eur. J. Org. Chem. 2002, 24, 4190-4194; Dep. Quim. Org., Fac. Farm., Univ. Complutense, E-28040 Madrid, Spain; Eng.) — Klein

15- 194

Page 2: Diastereoselective Synthesis of α-Methylpyroglutamates from α,β-Didehydro α-Amino Acids

2003 Amino acids


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