Publication

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

Manfred Schlosser
2003
Journal Articles

Abstract

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)]

Official source

https://infoscience.epfl.ch/entities/publication/165745fd-d30b-443a-ae9f-f35821a38a21

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Manfred Schlosser
2003
Journal Articles

Abstract

Official source

https://infoscience.epfl.ch/entities/publication/165745fd-d30b-443a-ae9f-f35821a38a21

About this result

Related concepts (31)

Organolithium reagent

In organometallic chemistry, organolithium reagents are chemical compounds that contain carbon–lithium (C–Li) bonds. These reagents are important in organic synthesis, and are frequently used to transfer the organic group or the lithium atom to the substrates in synthetic steps, through nucleophilic addition or simple deprotonation. Organolithium reagents are used in industry as an initiator for anionic polymerization, which leads to the production of various elastomers.

Wittig reaction

The Wittig reaction or Wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide called a Wittig reagent. Wittig reactions are most commonly used to convert aldehydes and ketones to alkenes. Most often, the Wittig reaction is used to introduce a methylene group using methylenetriphenylphosphorane (Ph3P=CH2). Using this reagent, even a sterically hindered ketone such as camphor can be converted to its methylene derivative.

Tert-Butyllithium

tert-Butyllithium is a chemical compound with the formula (CH3)3CLi. As an organolithium compound, it has applications in organic synthesis since it is a strong base, capable of deprotonating many carbon molecules, including benzene. tert-Butyllithium is available commercially as hydrocarbon solutions; it is not usually prepared in the laboratory. tert-Butyllithium is produced commercially by treating tert-butyl chloride with lithium metal. Its synthesis was first reported by R. B. Woodward in 1941.