Effect of Solvent and Temperature on the Lithium−Bromine Exchange of Vinyl Bromides: Reactions of n-Butyllithium and t-Butyllithium with (E)-5-Bromo-5-decene

Abstract

The outcome of reactions of (E)-5-bromo-5-decene (1), a representative vinyl bromide, with t-BuLi or n-BuLi at 0 degrees C and room temperature, respectively, in a variety of solvent systems has been investigated. Vinyl bromide 1 does not react with t-BuLi in pure heptane; however, the presence of even small quantities of an ether in a predominantly heptane medium resulted in virtually complete consumption of 1 at 0 degrees C, resulting in nearly the same distribution of products, including 60-80% of (Z)-5-decenyllithium, regardless of the solvent composition. Vinyl bromide 1 reacts slowly with n-BuLi at room temperature in a variety of ether and heptane-ether mixtures to afford a mixture of products including significant quantities of recovered starting material. The results of these experiments demonstrate that lithium-bromine exchange between a vinyl bromide and either t-BuLi or n-BuLi at temperatures significantly above -78 degrees C is not an efficient method for the generation of a vinyllithium.

Cyclizations of Alkynes: Revisiting Baldwin’s Rules for Ring Closure

“…Later, Myers and co-workers have utilized such regioselective closure of reactive species formed via Br–Li exchange at an endocyclic vinyl bromide adjacent to an ethynyl moiety in the development of synthetic approaches toward Kedarcidin and related natural products. These examples of 5-(σ-vinylendo)-exo-dig cyclizations gave the desired product in up to 52% (Scheme ) At the reported experimental conditions (−78 °C in THF), this reaction is believed to proceed through a carbanionic pathway. , …”

Doubly Diastereoconvergent Preparation and Microsolvation-Controlled Properties of (Z)- and (E)-1′-Lithio-1′-(2,6-dimethylphenyl)propenes

“…Again, the primary product ( E )- 1 , expected from ( Z )- 9 , was NMR-invisible because it had readily (<5 min at ≤ rt) and entirely been converted into unsolvated ( Z )- 1 . (The mechanism of this donor-free stereoinversion is unknown Table S11).…”