Reactions Using in situ Generated Organometallics

Deprotonation by in sita generated organoalkali metal reagents 

The preparation and immediate reaction of alkyllithium for deprotonation of various acidic compoimds precisely illustrate this aspect (Fig. 34).i 8 representative reaction is the quantitative formation in a few minutes of 2-lithio-1,3-dithiane by sonication of f-butyl chloride, lithium, and 1,3-dithiane in THF. In situ generated butyllithium was used for the deprotonation of alkynes and phosphonium salts. With secondary amines, the strongly basic lithium amides are produced (p. 368). This procedure avoids the use of organolithium auxiliaries with solvent and temperature adjustments. o The isotopically labeled Li hexamethyl disilazide was obtained by this method.i i 

A cascade reaction, the preparation of isobutyric acid dianion, was achieved by a one-pot sequence, the formation of butyllithium, deprotonation of di-i-propyl amine to LDA, then formation of the acid dianion. Quenching with benzal-dehyde gives the hydroxyacid in 78% yield. 2-Lithio-furan and -anisole were prepared and used in several synthetic reactions. some instances, it can be advantageous to replace THF by tetrahydropyran (THP), a solvent with a better stability in the presence of strong bases. 

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