The Chemistry of Carbenoids and Other Thermolabile Organolithium Compounds

Abstract

Organolithium compounds are thermally quite stable, despite their extremely high reactivity. Thermolability, i. e. the property of undergoing irreversible changes at low temperatures without the participation of molecules of a different kind, is associated with additional functional groups, which may be readily eliminated together with the metal cation, may cause intramolecular rearrangements, or may lead to intermolecular additions and substitutions involving several molecules of the same type. Thermolabile organolithium compounds have frequently been postulated or detected as intermediates of important reactions, and are therefore of theoretical and practical interest. If certain precautions are taken, it is occasionally possible (mainly at low temperatures) to prepare them intact, and hence to release them from the constraint of the fate assigned to them as short-lived intermediates. Investigations with this aim have for some time occupied a place of considerable importance in the chemistry of organometallic compounds.

Lithium Carbenoids

“…Again, this reaction does not only take place in vinylidene but also in alkyl carbenoids 30 . On the other hand, the intramolecular shift of a β-aryl, cyclopropyl or hydrogen substituent, known as the Fritsch-Buttenberg-Wiechell rearrangement, is a typical reaction of α-lithiated vinyl halides (reaction d) 2,3 . A particular carbenoid-like reaction occurring in α-halo-α-lithiocyclopropanes is the formation of allenes and simultaneous liberation of the corresponding lithium halide (equation 3) 41 -44 .…”

“…Thermal lability is typical of lithium carbenoids, the chemistry of which has been disclosed by the seminal work of Köbrich 2,3 . Another feature of lithium carbenoids is an ambiphilic behavior, which originates from the coexistence of an electron-donating and an electron-withdrawing substituent at the carbon center.…”

Mechanistic study of the reaction of vitamin B12s with 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane

“…Q@ C-H I dihalides with copper (13) among others (14), since the a-elimination will generate a carbene or carbenoid type intermediate which will readily rearrange to the products. Attempts to trap a free carbene using cyclohexene were unsuccessful, a result which was somewhat expected since DCS itself may act as a carbene trapping agent.…”

Preparation of fluorohalomethylmagnesium halides using highly active magnesium metal and their reactions

“…Early attempts to prepare fluoro-or fluorohalomethyl organometallic compounds using more electropositive metals, such as lithium or magnesium were unsuccessful due to immediate decomposition of the fluoroorganometallics formed to the corresponding carbenes and metal halides [6] and hence the name ''carbenoids'' was introduced for this class of compounds [7,8]. A major breakthrough was achieved by Kuroboshi et al, who successfully generated dibromofluoromethyllithium under Barbier conditions from tribromofluoromethane and butyllithium at À130 8C and reacted it with a series of electrophiles [9].…”