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Isomerisation of ( E )‐2‐Tetrahydrofurylidenealkanecarboxylic Esters and Amides into Their ( Z ) Isomers by Chelation Control with Metallated Bases or Lewis Acids
Author(s) -
Hanquet Gilles,
SalomRoig Xavier J,
Lemeitour Sonia,
Solladié Guy
Publication year - 2002
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 - 10.1002/1099-0690(200207)2002:13<2112::aid-ejoc2112>3.0.co;2-#
Subject(s) - chemistry , isomerization , lewis acids and bases , allylic rearrangement , chelation , steric effects , medicinal chemistry , stereochemistry , propionates , organic chemistry , catalysis
2‐(2‐Tetrahydrofurylidene)propionates, usually obtained only in the more stable ( E ) configuration 1 , were efficiently isomerised into their ( Z ) isomers 2 by use of Lewis acids or metallated bases. The ( E )/( Z ) isomerisation was governed by different factors (type of chelating agent, nature and steric demand of the α,β‐unsaturated group). We demonstrated that judicious selection of the α,β‐unsaturated group, in combination with the chelating agent, afforded yields of up to 95% with either LDA [R = N(Me) 2 , t Bu] or MgBr 2 and ZnI 2 (R = OBn), and that the reaction was also influenced by 1,3‐allylic strains. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)