Substitution Reactions of Organometallic Reagents

The reaction of phenyllithium and allyl chloride using label reveals the occurrence of allylic transposition. About three-fourths of the product results from bond formation at C(3) rather than C(l), which can be accounted for by a cyclic mechanism.  

The portion of the product formed by reaction at C(l) in allylic systems may form by direct substitution, but it has also been suggested that a cyclic TS involving an aryllithium dimer might be involved. 

These mechanisms ascribe importance to the Lewis acid-Lewis base interaction between the allyl halide and the organolithium reagent. When substitution is complete, the halide ion is incorporated into the lithium cluster in place of one of the carbon ligands. 

From a synthetic point of view, direct alkylation of lithium and magnesium organometallic compounds has been largely supplanted by transition metal-catalyzed processes. We discuss these reactions in Chapter 8 of Part B. 

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In this chapter, the substitution reactions of organometallic reagents with organic halides and related electrophiles are reviewed. - The major portion of the chapter is devoted to a discussion of organocopper compounds, which first transformed the alkylation of nonstabilized carbanions into a reaction of general synthetic utility. More recently, transition metals other than copper have also found widespread application in such coupling reactions, and developments in this area are outlined in Section 1.5.3. 

Conjugate Addition and Substitution Reactions of Organometallic Reagents... 

The Reaction of Organometallic Reagents with Epoxides 3(OCJ-seco-Alkyl-de-alkoxy-substitution... 

The reactions of organometallic reagents with haloorganogermanes provide general methods for the preparation of unsymmetrically substituted tetraorganogermanes (eq... 

When the pyridyl group is substituted on other positions of the ring, the reaction of organometallic reagents with alkyl 2-pyridylsulfoxides affords symmetrically substituted 2,2 -bipyridines76 8 7,88 (Table 3.7)... 

See [77] and [78] on the formation of pinacols from reactions of organometallic reagents with (substituted) benzophenones. Indeed benzopinacol was found [79] among the products of almost all the Barbier reactions listed in Tables 2.18 through 2.21 in Sect. 2.4.4. Radical formation on the surface of the metal is most likely the origin of such sideproducts. 

The addition of organometallic reagents to the carbonyl group of conveniently substituted aldonolactones constitutes a viable chain-extension method. The reaction leads to the formation of hemiacetals of glyculoses, 1-methylene sugars, and C-glycosyl compounds, which are precursors of, or occur as subunits of, a variety of natural products. 

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