Alkoxides reaction with trihalides

Williamson reaction The formation of an ether by the treatment of an alkyl halide with an alkoxide anion. Gem-dihalides react with alkoxides to give acetals, while 1,1,1-trihalides give ortho esters. 

It was then discovered that cations can also be generated from lithium alkoxides in the presence of boron trihalides. Thns, the reaction of a lithium alkoxide with phenylacetylene in the presence of boron trichloride generates ( , )-l-chloro-l,3,5-triphenyl-l,4-pentadiene in 78% yield, only 4% of (Z,fi)-l-chloro-l,3,5-triphenyl-l,4-pentadiene is formed (Scheme 23.75). Notably, the stereochemistry of the major prodnct obtained using this process is opposite that of the product from the reaction shown in Scheme 23.70. 

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