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Zinc Salt Promoted Diastereoselective Synthesis of Chiral Propargylamines Using Chiral Piperazines and Their Enantioselective Conversion into Chiral Allenes
Author(s) -
Periasamy Mariappan,
Reddy Polimera Obula,
Edukondalu Athukuri,
Dalai Manasi,
Alakonda Laxman M.,
Udaykumar Bantu
Publication year - 2014
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201402766
Subject(s) - chemistry , enantioselective synthesis , chiral derivatizing agent , chiral auxiliary , allene , zinc , imine , bromide , organic chemistry , combinatorial chemistry , medicinal chemistry , catalysis , enantiomer , chiral column chromatography
Zinc chloride catalyzed reactions of chiral piperazine derivatives 4a – d with 1‐alkynes and aldehydes give chiral propargylamines in 67–95 % yields with up to 99:1 dr . The chiral propargylamines are converted into chiral allenes by using zinc bromide in short reaction times (1–2 h) in high enantioselectivities (up to 99 % ee ) in good yields (up to 89 %). The chiral piperazines are recovered in good yields (79–86 %) by reduction of the imine byproducts in situ by using NaBH 4 . Unexpectedly, the chiral aryl‐substituted allenes undergo facile cyclodimerization under neat conditions at 25 °C, in contrast to an earlier report that cyclodimerization takes place at 80 °C in benzene, which further illustrates the importance of the two‐step procedure reported herein because the chiral propargylamine may be converted into chiral allene when required.