Organolithium and-magnesium Compounds

1 Organolithium and -magnesium compounds. Compared with extensive studies carried out on the Ni-catalyzed transmetallation reaction of Grignard reagents[43I,432], few examples of the Pd-catalyzed reactions of Mg are 

The Li compound 588 formed by the ort/io-lithiation of A. A -dimethylaniline reacts with vinyl bromide to give the styrene derivative 589(433]. The 2-phe-nylindole 591 is formed by the coupling of l-methyl-2-indolylmagnesium formed in situ from the indolyllithium 590 and MgBr2, with iodobenzene using dppb[434]. 2-Furyl- and 2-thienyllithium in the presence of MgBr2 react with alkenyl halides[435]. The arylallenes 592 and 1,2,4-alkatrienes are prepared by the coupling reaction of the allenyllithium with aryl or alkenyl halides[436]. 

The coupling of alkyl Grignard reagents with alkyl iodides to afford alkanes by use of dppf as a ligand has been reported[449], but re-examination of the reaction has shown that only reduction takes place, and no coupling was observed[450]. 

Regiocontrolled q- or / -alkenylation and arylation of cyclic enones are possible without protection of the ketone by applying the coupling reaction of the Q- or /3-halo enones 607 and 608 with aryl and alkenylzinc reagents[468,469]. 

Triflates are used for the reaction[470]. The 5-phenyltropone 609 is prepared by coupling of the triflate with phenylzinc chloride[471]. Instead of the expensive triflale, phenyl fluoroalkanesulfonate as a triflate equivalent is used for coupling[472]. Phenyl fluorosulfonate (610) is another reagent used for cou-pling[473]. 

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A general method for the synthesis of organomercurials is the transmetallation of mercury (II) salts with other organometallic species. Organolithium and -magnesium compounds continue to be widely employed for the preparation of complexes with formula RHgX or HgR2 (see equation 1). 

Reetz has shown that hydride acceptors (e.g. triphenylmethyl tetrafluoroborate) may effect elimination of /8-hydrogen atoms from organolithium and magnesium compounds, to generate olefins under mild conditions.Yields increase from primary through to tertiary metallated compounds. Furthermore, addition of alkyl-lithium reagents to activated olefins (e.g. 1,1-diphenylethylene) followed by hydride abstraction gives the 2-alkyl-l,l-diphenylalkenes. ... 

Bogdanovic, B. (1985) Catalytic synthesis of organolithium and magnesium compounds and of lithium and magnesium hydrides. Angew. Chem. Int. Edn), 24, 262. 

There are several useful means for preparation of organomercury compounds. The general metal-metal exchange reaction between mercury(II) salts and organolithium or magnesium compounds is applicable. The oxymercuration reaction discussed in Section... 

Alkyltrisidialkylamino)titanium derivatives, R Ti(NR2)3. ) These reagents are readily available by reaction of halotris(dialkylamino)titanium with organolithium or -magnesium compounds. The reagents, prepared in situ in ether, react with nonenolizable aldehydes to give tertiary amines (1), possibly via an iminium salt (equation I). With enolizable aldehydes and ketones, the reaction results in enamines after nonaqueous workup. 

In view of the trend to more controlled and stereoselective reactions with readily available, less expensive and environmentally non-problematic reagents, the light-induced inner-sphere electron transfer between M-C bonds of less polar co-ordinating organometallics (Zn, Al) and the organic substrate seems to be a particularly attractive alternative to thermal reactions from organolithium or -magnesium compounds. 

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