Lead organolithiums

The reaction with organolithium or organomagnesium reagents 9 leads to formation of /3-aminoalcohols 10 ... 

The equatorial selectivity observed with organolithium reagents is enhanced in diethyl ether as the reaction solvent by the addition of lithium perchlorate (Table l)12. I3C-NMR studies47 indicate that the formation of a complex between lithium perchlorate and the carbonyl group, which also leads to a dramatic enhancement of the rate of the addition reaction, accounts for the increased diastereoselectivity. 

Preliminary experiments prove that the substitution pattern of the /V-aryl moiety of imine 1 is crucial for the stereoselectivity of this reaction. The 2-substituent on the aryl group is of special importance. Namely, introduction of a methoxy group leads to a considerable decrease of enantioselectivity compared to the corresponding 2-H derivative, probably due to disfavor-able coordination with the organolithium complex. In contrast, alkyl groups show the reverse effect along with increased bulkiness (e.g., Tabic 1, entries l-3a) but 2,6-dimethyl substitution provides lower ee values. Furthermore, the 4-substituent of the TV-aryl moiety is of minor importance for the stereoselectivity of the reaction [the Ar-phcnyl and the /V-(4-methoxyphenyl) derivatives give similar results], whereas a substituent in the 3-position results in lower stereoselectivities (e.g., Et, Cl, OCHj)41. 

Next to the formation of Grignard reagents, the most important application of this reaction is the conversion of alkyl and aryl halides to organolithium compounds, but it has also been carried out with many other metals, (e.g., Na, Be, Zn, Hg, As, Sb, and Sn). With sodium, the Wurtz reaction (10-93) is an important side reaction. In some cases, where the reaction between a halide and a metal is too slow, an alloy of the metal with potassium or sodium can be used instead. The most important example is the preparation of tetraethyl lead from ethyl bromide and a Pb—Na alloy. 

Addition of Grignard reagents or organolithium reagents to co-halo nitriles leads to 2-substituted cyclic imines. 

An early example of the use of a subcatalytic amoimt of sparteine for the activation of an organolithium nucleophile was reported by Lautens et al. in the carbometallation of a meso-unsaturated oxabicycle 25, with ring opening leading to the substituted cycloheptene derivative 26 (Scheme 4) [4]. Both yield and enantiomeric excess remained virtually unchanged when the ratio n-BuLi sparteine was lowered to 1 0.15. However, when a 3 mol% amount of the ligand 1 was used, a 20% decrease in enantioselectivity was observed. 

The rearrangement in Entry 9 occurs spontaneously on warming of the reaction mixture from addition of an organolithium reagent to form the vinyl carbinol unit. This is a very general means of constructing reactants for oxy-Cope rearrangements that leads... 

Organomagnesium and organolithium compounds are strongly basic and nucleophilic. Despite their potential to react as nucleophiles in SN2 substitution reactions, this reaction is of limited utility in synthesis. One limitation on alkylation reactions is competition from electron transfer processes, which can lead to radical reactions. Methyl and other primary iodides usually give the best results in alkylation reactions. 

One of the most interesting reactions of this type involves the intramolecular addition of the organolithium derivative to the aryne (13) which is derived from the dilithio-compound (12) 28>. This leads to the remarkably stable organolithium compound (14) which reacts with water to form the expected heptafluorobiphenylene, and with bromine to form 1-bromoheptafluorobiphenylene. 

Cyanocuprates constitute a class of organocopper compounds that finds applications in organic synthesis.234 They are prepared by the direct reaction of an organolithium reagent and CuCN, with two different types of compounds being prepared depending on the stoichiometry employed the 1 1 ratio leads to RCu(CN)Li compounds whereas the 2 1 mixture affords R2Gu(GN)Li2. The lower- order or 1 1 cyanocuprates usually display the Cu-C-N-Li... 

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