Regioselective 1,4-addition to .alpha.,.beta.-unsaturated ketones with Grignard reagents mediated by (N,N,N',N'-tetramethylethylenediamine)zinc(II) chloride

Abstract

The reaction of ,/3-unsaturated ketones with a THF solution of RMgX (3 mol equiv) and ZnCLyTMEDA (1 mol equiv) followed by NH4C1 gave 1,4-addition products. The products were contaminated by 1,2-addition products when R = Ph and Me but were essentially free of those compounds when R = n-Bu or i-Pr. The yields were highest when X = Cl. Thus the reaction of 2-cyclohexen-1 -one with a solution of n-BuMgCl and ZnCl2-TMEDA gave 3-n-butylcyclohexanone (1) in 96% yield.

Conjugate additions of grignard reagents to α,β-unsaturated ketones mediated by diamine zinc(II)monoalkoxides

“…yields reported for trialkylzincates. (6) Arylgrignards gave low yields in the 1,4-addition reaction using our procedure. Furthermore the use of THF instead of diethylether strongly increases the yield (entries 2,10).…”

“…Furthermore these authors found that a reagent (presumably a triorganozincate), prepared from 3 equivalents of Grignard reagent and 1 equivalent of ZnCl 2 /N,N,N',N'-tetramethylethylenediamine complex (TMEDA.ZnCl 2 ) gave 1,4-addition products. (6) A disadvantage of the latter system as compared to cuprates is the loss of two equivalents of the alkylligand to be transfered. In connection with our studies on selective organometallic addition reactions (7) we investigated the zinc-mediated 1,4-addition of Grignard reagents and report now a new procedure using alkoxides as non transferable ligands for the zinc complexes.…”

Ligand‐Activated Lithium‐Mediated Zincation of N‐Phenylpyrrole

“…ZnCl 2 ·TMEDA was prepared by using a described procedure. [33] Nuclear magnetic resonance spectra were acquired on a Bruker ARX 200 spectrometer (200 MHz and 50 MHz for 1 H and 13 C, respectively). Chemical shifts are given in ppm as d values relative to tetramethylsilane.…”

2.06 Formation of Enolates

“…209 A similar type of reaction has been conducted with ZnCl 2 -TMEDA and 3 equivalents of a variety of Grignard reagents. 210 The experiments offer no real evidence for the existence of R 3 ZnMgX (X ¼ CI, Br). The formula 'R 3 ZnMgX' denotes only the stoichiometry involved in preparing the solutions used.…”