Organolithium reagents basicity

Organoboranes, 228, 230-233 Organocopper compounds. See Lithium diorganocuprates Organolithium reagents basicity of, 551-553, 570 preparation of, 549-550, 571 reaction of... 

Although the C-3 stereocenter in 6 may be susceptible to epimer-ization in the presence of a basic organolithium reagent, enal 6 condenses smoothly in the desired and expected way with lithio sul-fone 5 at -78 °C to give, after quenching with acetic anhydride, a stereoisomeric mixture of acetoxy sulfones (see 35, Scheme 7). ( ,E,7f)-Triene 36 is then unveiled on reduction of the stereoisomeric acetoxy sulfones with 5 % sodium amalgam (77 % overall yield from 6).3... 

The phosphoranes (14) readily undergo ligand exchange on treatment with organolithium reagents. Thus, (14 R = Ph) with butyl-lithium gave an almost quantitative yield of (14 R = Bu) whereas with the less basic methyl-lithium equilibrium was established between (14 R = Ph) and (14 R = Me). 

Organolithium reagents have also been employed for the synthesis of novel bis(alkynyl)mercury derivatives. These include Hg(C=CCF3)263 and 46-48,64 which have been synthesized along with the bis(alkynyl)aurate analogs. Bis(alkynyl)mercury species such as 49 can also be obtained by reaction of monosubstituted alkynes with K2[Hgl4] in basic aqueous solutions.6 ... 

How well an organolithium reagent fares as an exchange component depends on its basicity. Thus, tert-butyllithium outperforms iec-butyllithium, which in turn is superior to butyllithium. MethyUithium is the least reactive alkyllithium but still surpasses phenyl-lithium, at least at low concentrations, i.e. the order is ... 

From the practical piont of view however, due to other favorable possible pathways a- or -deprotonation) as depicted above, it is interesting to differentiate between simple organolithium reagents, which show a high basicity, and stabilized organolithium reagents, with a lower basicity, but also a moderate nucleophihcity. In many cases, activation of the reaction can be obtained by the addition of a strong Lewis acid. 

B. Oxirane Ring Opening with Low Basicity Organolithium Reagents... 

R—MgX ch3ch 1 reagents and organolithium reagents) proceeds to stage 1 and follows the basic conditions mechanism. 

Reactions of Esters Esters are much more stable than acid chlorides and anhydrides. For example, most esters do not react with water under neutral conditions. They hydrolyze under acidic or basic conditions, however, and an amine can displace the alkoxyl group to form an amide. Lithium aluminum hydride reduces esters to primary alcohols, and Grignard and organolithium reagents add twice to give alcohols (after hydrolysis). 

Reactivity. The basicity of organolithium reagents decreases with increasing stability of the carbanion moiety (e.g., t-BuLi > 5-BuLi > n-BuLi). 

A recent report describes the use of magnesium (2-ethoxy)ethoxide as an additive in reactions to prepare organolithium reagents. The additive moderates the basicity of the prepared anion and prevents unwanted side reactions, for example with the solvent. 

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