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Synthesis and Desymmetrization of meso ‐2,3‐Diphenylpiperazine for Application in Asymmetric Transformations
Author(s) -
Periasamy Mariappan,
Edukondalu Athukuri,
Ramesh Eagala
Publication year - 2017
Publication title -
chemistryselect
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.437
H-Index - 34
ISSN - 2365-6549
DOI - 10.1002/slct.201700488
Subject(s) - diastereomer , desymmetrization , chemistry , oxalic acid , ethyl chloroformate , yield (engineering) , hydrolysis , toluene , enantiomer , chloroformate , enantiomeric excess , medicinal chemistry , organic chemistry , enantioselective synthesis , catalysis , materials science , metallurgy
The meso ‐2,3‐diphenylpiperazine was prepared in 86 % yield with 99:1 dr from the readily accessible 5,6‐diphenyl‐2,3‐dihydropyrazine by NaBH 4 /MeOH reduction. The corresponding diastereomeric amides prepared using ( R )‐(‐)‐menthyl chloroformate, after separation, benzylation and hydrolysis gave both isomers of optically active N ‐benzyl‐2,3‐diphenylpiperazine samples in up to 94 % ee which after further enrichment using the simple achiral oxalic acid afforded samples of both enatiomers in 99 % ee . Reaction of the chiral optically active N ‐benzyl‐2,3‐diphenylpiperazine with terminal alkynes and aldehydes in the presence of ZnCl 2 gave the corresponding propargylamines with very high diasterioselectivities (up to 99:1 dr ) from which both enantiomers of chiral allenes were obtained in up to 82–86 % ee by reaction with ZnBr 2 in toluene at 120 °C.