Lithium bromide reaction with mesylates

From alcohols. Alcohols can be transformed into phenylselenides in a stepwise manner via mesylation and reaction with lithium phenylselenolate. This procedure offers obvious advantages over the formation of the corresponding bromides or iodides when subsequent reaction with strong nucleophiles, such as organolithium compounds, are necessary to prepare the radical precursors. The diol 8 is converted to the bis(phenylselenide) 9 via the corresponding bis(mesylate) as shown in Scheme 2 [6]. Compound 9 is converted to the radical precursor 11 via reaction with lithium phenylacetylide followed by alkylation with allylbromide and a Pauson-Khand reaction. Such a reaction sequence would not be feasible with an alkyl halide. The cyclization afforded the expected tricyclic compound 12 in 95% yield. 

In the laboratory of J. Zhu, the synthesis of the fully functionalized 15-membered biaryl-containing macrocycle of RP 66453 was accomplished. One of the key steps in their approach was Corey s enantioselective alkylation of a glycine template with a structurally complex biaryl benzyl bromide. This benzyl bromide was prepared from the corresponding benzyl mesylate via the Finkelstein reaction using lithium bromide in acetone. 

Reduction of losylates. Reaction of primary or secondary tosylates or mesylates with sodium iodide and zinc powder in refluxing glyme (or DMSO, HMPT) results in reductive cleavage (equation I). Lithium bromide is less efficient. ... 

Suyama and Gerwick reported a shorter, more practical route to both enantiomers of epiquinamide from the commercially available L-omithine derivative 2127 or its enantiomer.The route to (+)-epiquinamide (2104) is illustrated (Scheme 268). After conversion of 2127 into the Wein-reb amide (—)-2128, reaction with aUylmagnesium bromide produced the ketone (+)-2129, which required no purification apart from washing and extraction. Highly diastereoselective chelation-controUed reduction with lithium tri(teft-butoxy) aluminum hydride followed by mesylation gave the crystalline mesylate (—)-2130, which also did not require chromatographic... 

Treatment of the allylic mesylate (5) with various alkyl or alkynyl Grignard reagents gave mainly the products of direct displacement, whereas methylmagnesium bromide afforded the a,p-products of S 2 reaction (Scheme 5). Lithium dimethyIcuprate, on... 

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