Lithium reagents, use

Both reagents 7 and 9 are also excellently suited for the introduction of 3-substituted allyl residues. Both high simple anti) diastereoselectivity and enantioselectivity are observed, irrespective of the configuration of the double bond in the allylmagnesium, -potassium, or -lithium reagent used for the in situ preparation 11,35 36. 

Each of the following compounds gives products in which one or more lithium atoms have been introduced under the conditions specified. Predict the structure of the lithiated product on the basis of structural features known to promote lithiation and/or stabilization of lithiated species. The number of lithium atoms introduced is equal to the number of moles of lithium reagent used in each case. 

The extent of olefin formation depends on the position of the functional group, " on the degree of a-substitution and on the concentration of the hydride (or deuteride). Usually olefin formation can be largely suppressed by increasing the concentration of lithium aluminum deuteride. With certain tosylhydrazones, however, such as the C-17 derivative (103), olefin (104) is a major product irrespective of the quantity of the reagent used. ... 

All that has been said in this section applies with equal force to the use of organo-lithium reagents in the synthesis of alcohols. Grignard reagents are one source of nucleophilic carbon organolithium reagents are another. Both have substantial carbanionic char acter in their- car bon-metal bonds and undergo the same kind of reaction with aldehydes and ketones. 

Allylstannanes can be prepared by treatment of allyl halides with trialkyl- or triaryltin lithium reagents. Displacement of primary allyl halides tends to be regioselective for formation of the less substituted allylstannane, and takes place with useful retention of double-bond geometry14-16. 

Isoquinoline 53 was also used as a substrate for the addition of organo-lithium reagents by Alexakis and Amiot (Scheme 13) [13]. While remaining quite modest, the best enantioselectivities (48%) were still reached with sparteine after quenching with methyl chloroformate. However, a mixture of mono- and bisacylated products 54 and 55 were obtained in all cases and the use of a catalytic amount of sparteine lowered the selectivity of the adducts. 

The vinyl lithium reagents generated in the Shapiro reaction can be used in tandem reactions. In the reaction shown below, a hydroxymethyl group was added by formylation followed by reduction. 

Preparation Using Metallic Lithium. Most simple organolithium reagents can be prepared by reaction of an appropriate halide with lithium metal. The method is applicable to alkyl, aryl, and alkenyl lithium reagents. 

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