Organolithium compounds, conductivities

Although the resulting vinylallenes 48 were usually obtained as mixtures of the E and Z isomers, complete stereoselection with regard to the vinylic double bond was achieved in some cases. In addition to enyne acetates, the corresponding oxiranes (e.g. 49) also participate in the 1,5-substitution (Scheme 2.18) and are transformed into synthetically interesting hydroxy-substituted vinylallenes (e.g. 50) [42], Moreover, these transformations can also be conducted under copper catalysis by simultaneous addition of the organolithium compound and the substrate to catalytic amounts of the cuprate (see Section 3.2.3). 

As is implicit in the fact that the products of the (stoichiometric) 1,6-cuprate addition - the lithium allenyl enolate and the organocopper compound - are formed as independent species, it is also possible to conduct the reaction catalytically through in situ regeneration of the cuprate. The reaction can thus be run in a continuous mode, with only catalytic amounts of the preformed cuprate being necessary (with simultaneous addition of the substrate and the organolithium compound) enabling the desired allenes to be prepared even on larger scales (Eq. 4.17) [3oj. 

The reaction of Grignard reagents and organolithium compounds with aldehydes and ketones is perhaps the most useful method for the preparation of alcohols. The reaction is conducted under basic conditions and proceeds according to the following general mechanism ... 

In part (2), the reaction was conducted at -40 . At this low temperature, organolithium compounds will not react with ether at an appreciable rate. Hence the initial product is t-butyllithium. Carbonation of this will yield trimethylacetic acid. 

Methyllithium is a strong basic and a powerful nucleophile. Compared to another synthetically important organolithium compound, -butyllithium, methyllithium reacts slowly with tetrahydrofuran at room temperature. An etheral solution of methyllithium is stable for a long time. Most of the reactions involving methyllithium are conducted at low temperatures. Methyllithium is used for deprotonations and as a source of methyl anion. Ketones can be converted to tertiary alcohols using methyllithium as... 

Because the reactions of related in -cyclohexadienyl complexes are synthetically valuable, the reactions of this ligand have been studied extensively. An outline of how this chemistry can be conducted on the Fe(CO)j fragment is shown in Equation 11.51. A variety of cyclohexadienes are readily available from Birch reduction of substituted aromatics. Coordination and abstraction of a hydride, typically by trityl cation, leads to cationic cyclohexadienyl complexes. These cyclohexadienyl complexes are reactive toward organolithium, -copper, -cadmium, and -zinc reagents, ketone enolates, nitroal-kyl anions, amines, phthalimide, and even nucleophilic aromatic compounds such as indole and trimethoxybenzene. Attack occurs exclusively from the face opposite the metal, and exclusively at a terminal position of the dienyl system. This combination of hydride abstraction and nucleophilic addition has been repeated to generate cyclohexa-diene complexes containing two cis vicinal substituents. The free cyclohexadiene is ttien released from the metal by oxidation with amine oxides. ... 

Reaction with Organolithium Reagents. Organolithium derivatives of a variety of heteroaromatics have been fluorinated with NFSi. The direct C-H lithiation at the most reactive position of heteroarene compounds was conducted at low temperature with either t-BuLi, w-BuLi, or LDA in the presence of NFSi to provide regioselective fluorination. This way, oxazoles (eq 34), benzo[i>]thiophene-5,6-dicarbaldehyde, spiro[4,5-dihydrothieno[2,3-c]pyran-7,4 -piperidine, dibenzo-... 

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