Sequestered alkyllithiums: why phenyllithium alone is suitable for betaine-ylide generation

The key step in the trans-selective modification of the Wittig reaction is the a-lithiation of the lithium bromide coordinated ylide-aldehyde adduct (the so-called \"P-betaine\"). The olefination reactions were carried out for RCHO and [R1CH2PPh3]Br (R = C6H3, Ph, CH2:CMe, iPr, tBu; R1 = Bu, Pr, PhCH2CH2, C5H11) applying PhLi, MeLi, BuLi, sec-BuLi and tert-BuLi as bases. Only PhLi and MeLi yielded (E)-alkenes with good stereoselectivity (>98%), whereas other organolithium bases yielded (E)-(Z)-mixts. Special expt. with (C6D5)3P showed, that phenyllithium acts solely as base, forming a-lithiated betaine, and no P-Ph addn. intermediates were formed. Only phenyllithium effects this deprotonation rapidly and cleanly. Alkyllithiums (in particular, butyl-, sec-butyl-, and tert-butyllithium) react only sluggishly and incompletely, being tied up in very stable mixed aggregates with the lithium alkoxide part of the betaines. The different results of the Wittig reaction are accounted to the low aggregation ability of PhLi and (MeLi)4, which disfavors the formation of mixed product-base aggregates. [on SciFinder (R)]


Published in:
Chemistry - A European Journal, 9, 2, 570-574
Year:
2003
Keywords:
Note:
CAN 139:6948 29-7 Organometallic and Organometalloidal Compounds Institut de Chimie Organique, Universite, BCh,Lausanne,Switz. Journal 0947-6539 written in English. 532932-92-6P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (Wittig reaction, deuterium labeling; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 600-36-2 Role: RGT (Reagent), RACT (Reactant or reagent) (complexing agent, lithium base deactivation; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 1779-51-7 (Butyltriphenylphosphonium bromide); 4762-26-9 (Hexyltriphenylphosphonium bromide); 7484-37-9 (Triphenyl(3-phenylpropyl)phosphonium bromide); 21406-61-1 (Pentyltriphenylphosphonium bromide) Role: RCT (Reactant), RACT (Reactant or reagent) (deprotonation, olefination; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 1076-43-3 (Deuterobenzene) Role: RCT (Reactant), RACT (Reactant or reagent) (lithiation, iodination, deuterium labeling; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 109-72-8 Role: RCT (Reactant), RGT (Reagent), RACT (Reactant or reagent) (olefination product; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 7206-16-8P; 16002-93-0P; 37904-42-0P; 38206-55-2P; 51090-06-3P Role: SPN (Synthetic preparation), PREP (Preparation) (olefination product; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 78-84-2 (Isobutyric aldehyde); 78-85-3 (Methacrolein); 100-52-7 (Benzaldehyde); 111-71-7 (Heptanal); 630-19-3 (Pivalaldehyde) Role: RCT (Reactant), RACT (Reactant or reagent) (olefination; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 19549-70-3P Role: BYP (Byproduct), PREP (Preparation) (organolithium addn. product, side product; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 591-51-5; 594-19-4 (tert-Butyllithium); 598-30-1 (sec-Butyllithium); 917-54-4 Role: RGT (Reagent), RACT (Reactant or reagent) (stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 24762-44-5P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (triphenylphosphine deuterium labeling, quaternization; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases); 7379-67-1P Role: RCT (Reactant), SPN (Synthetic preparation), PREP (Preparation), RACT (Reactant or reagent) (triphenylphosphine deuterium labeling; stereoselectivity and mechanism of trans-selective Wittig olefination of aldehydes with salt-contg. organolithium bases)
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 Record created 2006-03-03, last modified 2018-01-27


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