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Über Katalysatoreffekte bei Umsetzungen α,β‐ungesättigter Ketone und Ester mit Haloformen unter Phasenstransfer‐Katalyse
Author(s) -
Dehmlow Eckehard V.,
Wilkenloh Jiirgen
Publication year - 1990
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19901230325
Subject(s) - chemistry , stereospecificity , catalysis , medicinal chemistry , ketone , steric effects , michael reaction , organic chemistry
Catalyst Effects on Reactions of α, β‐Unsaturated Ketones and Esters with Haloforms under Phase‐Transfer Catalysis Reactions of acceptor‐substituted alkenes with haloform/sodium hydroxide and PT‐catalyst result in dihalocarbene additions competitive to Michael additions, with or without consecutive cyclization, and further reactions. Product compositions are strongly dependent on the nature of the phasetransfer catalyst: Sterically unhindered quaternary ammonium ions and benzo‐crown ethers favour processes via carbenes, large delocalized (soft) cations foster primary Michael additions. Thus, tert ‐butyl cis ‐crotonate is dichlorocyclopropanated stereospecifically with NMe 4 Cl. The respective stereospecific CBr 2 conversion is successful only with PhHgCBr 3 .