Alkylithium reagents

Vinylic sulfones undergo the same reaction especially when allylic, benzylic or t-alkylithium reagents are employed. One case of a vinyl sulfone deserves special mention - . When phenyl trans-3-bromopropenyl sulfone is treated with certain Grignard reagents it undergoes an alkylating cyclization ... 

Nonstabiiized lithiooxiranes can be prepared by the reaction of strong bases such as alkylithium reagents or lithium amides. However, as already discussed in a preceding section (Section II), the competition between a- and /3-deprotonation has to be adressed, and the issue of this competition is highly dependent on the structure of the starting oxirane as well as on the nature of the base used. These lithiooxiranes are very reactive species. In order to prevent their decomposition, they can be stabilized by a diamine ligand. Further stabilization can be obtained by a remote functionality. 

The direct conversion of dialkyl sulfates into alkylithium reagents provides an alternative route to the R-OH -> R-X - R-Li method. 

Tosylhydrazones on reaction with alkylithium reagents give olefins in high yield. This new synthesis allowed for exas le the preparation of 16-androstene from androstan-17-one in quantitative yield.Reduction of carbonyl functions to methylene c ui be effected electrochemically or by treatment of the steroid ketones with powdered zinc in acetic anhydride saturated with hydrogen chloride at room temperature." ... 

By the extension of the above-mentioned stereoselective asymmetric addition of alkylithiums to other organolithium reagents such as lithium salts of methyl phenyl sulfide, 2-methylthiazoline, trialkylsilylacetylene, N-nitroso-dimethylamine, and acetonitrile, chiral oxiranes (95) U1), thiiranes (96) nl), acetylenic alcohols (98) 112), and amino alcohols (97) U1) were readily obtained. 

A more general method for arylation of terminal alkynes as well as electron-deficient alkynes is the Negishi Pd-catalyzed cross-coupling of aryl halides with alkynyl-zinc reagents. When using functionally substituted alkynylzincs, the deprotonation of 1-alkynes must be done with LDA instead of alkylithiums. 

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