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A novel L ‐neopentylglycine derivative as auxiliary for copper‐catalyzed asymmetric Michael reactions
Author(s) -
Christoffers Jens,
Schuster Katja
Publication year - 2003
Publication title -
chirality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.43
H-Index - 77
eISSN - 1520-636X
pISSN - 0899-0042
DOI - 10.1002/chir.10293
Subject(s) - chemistry , enamine , michael reaction , methyl vinyl ketone , ketone , isopropyl , catalysis , amide , selectivity , yield (engineering) , medicinal chemistry , derivative (finance) , aldol reaction , stereochemistry , organic chemistry , materials science , metallurgy , economics , financial economics
L ‐Neopentylglycine diethylamide ( 4a ). was prepared from the new unnatural amino acid L ‐neopentylglycine ( 1 ). The utilization of amide 4a as a chiral auxiliary in the copper(II)‐catalyzed asymmetric Michael reaction was investigated in comparison with L ‐valine diethylamide ( 4b ). Cyclic β‐oxocarboxylates 7 react with 4a and 4b to give the respective enaminoesters 8 , which were converted with methyl vinyl ketone (9) in the presence of 10 mol% Cu(OAc) 2 · H 2 O at room temperature in acetone to yield the optically active Michael addition products ( R )‐ 10a, b with high selectivity independent of the starting enamine. In the case of the seven‐membered β‐oxocarboxylate 7c, however, the valine‐derived enamine 8f led to higher enantioselectivity for product 10c. Despite the bulkiness of the neopentyl group, the isopropyl group with an α‐branch has a better stereoinducing effect. Chirality 15:777–782, 2003. © 2003 Wiley‐Liss, Inc.