Organolithium reagents, preparation

This complex should be used when the organolithium is in solution in a hydrocarbon solvent. For organolithium reagents prepared in ether (see Note 4), the same complex may be used or, more conveniently, copper iodide (Cull can be used. The Cul purchased from Prolabo or Merck 4 Company, Inc. may be used directly. Other commercial sources of Cul (Fluka, Aldrich Chemical Company, Inc., Alfa Products, Morton/Thiokol, Inc.) furnish a salt which affords better results when purified. 1 mol of Cul is stirred for 12 hr with 500 ml of anhydrous tetrahydrofuran, then filtered on a sintered glass funnel ( 3), washed twice with 50 ml of anhydrous tetrahydrofuran, once with 50 ml of anhydrous ether and finally dried under reduced pressure (0.1 imO for 4 hr. 

OrganometalUc reagents, prepared from fluorohalocarbons, including Grig-nard reagents [52] or organolithium reagents prepared by transmetaUation [50], are silylated with readily a variable alkylchlorosilanes (equations 70 and 71). 

Najera, J. M. Sansano, M. Yus, Recent Synthetic Uses of Functionalized Aromatic and Heteroaromatic Organolithium Reagents Prepared by Non-Deprotonating Methods, Tetrahedron 2003, 59, 9255— 9303. 

Synthetic uses of functionalized heteroaromatic organolithium reagents prepared by non-deprotonating methods 03T9255. 

Najera C, Sansano JM, Yus M (2003) Recent synthetic uses of functionalised aromatic and heteroaromatic organolithium reagents prepared by non-deprotonating methods. Tetrahedron 59 9255-9303... 

Carbocyclic substitution can also be achieved by first introdueing a reactive organomelallic substituent. Preparation of organolithium reagents can be done by one of the conventional melhods. especially halogen-metal exchange or directed lithiation. Table 14.2 gives examples. 

R Tl compounds, eg, methyl [3003-15-4], ethyl [687-82-1], isobutyl [3016-08-8], and phenyl [3003-04-1] thaHium(III), are usuaHy prepared by the reaction between a dialkyl or diarylthaHium haHde and an organolithium reagent in ether (16) ... 

Organolithium compounds are sometimes prepared in hydrocarbon solvents such as pentane and hexane, but nonnally diethyl ether is used. It is especially important that the solvent be anhydrous. Even trace amounts of water or alcohols react with lithium to form insoluble lithium hydroxide or lithium alkoxides that coat the surface of the metal and prevent it from reacting with the alkyl halide. Furthennore, organolithium reagents are strong bases and react rapidly with even weak proton sources to fonn hydrocarbons. We shall discuss this property of organolithium reagents in Section 14.5. 

The enantiomerically pure vinylic organolithium reagent 8 is prepared from (A )-ethyl lactate in four steps. Subsequent addition of A-mesitylsulfonylimines 7 (they provide better diastereo-selectivilies than the corresponding jV-Losylimines) at — 110°C in tetrahydrofuran affords the adducts 9a and 9b in moderate yields (20-63%) but high diaslereoselectivities (d.r. 96 4 — 98 2)l0. 

In order to prove the utility of this method and to ascertain the absolute configuration of the products, (S)-alanine has been enantioselectively prepared. The key step is the addition of methyllithium to the AjA -dimethyl hydrazone acetal 4c, derived from diol 3c. In accordance with 13C-NMR investigations it can therefore be assumed that all major diastereomers resulting from the addition of organolithium reagents to hydrazone acetals 4a-c derived from diols 3a, 3b or 3c (Table 3, entries 1 -6) have an S configuration at the newly formed stereogenic center. 

Germyl, Stannyl, and Plumbyl Anions The preparative methods for the synthesis of the germyl, stannyl, and plumbyl anions are essentially the same as those mentioned above for the silyl anions. The most widely used methods are (1) reduction of halides R3EX (R = alkyl, aryl E = Ge, Sn, Pb X = Cl, Br) with alkali metals and (2) reductive cleavage of the E-E bond of R3E-ER3 (R = alkyl, aryl E = Ge, Sn, Pb) with alkali metals or organolithium reagents. Due to the favorable polarization of the (E = Ge, Sn, Pb) bond, the direct metalation... 

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