Alkoxy dehalogenation

Vinylic halides also undergo high yielding alkoxy dehalogenation using copper(I) salts as catalysts in a mixed methanol/A-methylpyrrolidine solvent system245. The reaction proceeds with retention of the double-bond geometry (equation 29) and multi-halo vinyl halides may be used. 

In the presence of AIBN, tributyltin hydride is an excellent dehalogenating reagent for generating radicals. The bromoalkylcyclobutanone 206 undergoes reductive ring expansion to give, via the annealed alkoxy radical, the cis-fiised bicycle 207 stereospecifically as the major product [113], (Scheme 81)... 

Direct photolysis of 2-halopyridines in methanol, ethanol or acetonitrile (with 1% water) affords pyridine, together with alkoxy-, or hydroxypyridines376. The formation of the substitution products will be discussed in Section IV.C. The reductive dehalogenation is considered to proceed via homolysis of the carbon-halogen bond. The efficiency of pyridine formation decreases in the order Br > Cl > I. The 3- and 4-halopyridines produce pyridine exclusively. 

The presence of amino, hydroxy, alkoxy, or carboxy groups on the ring facilitates the dehalogenation of a phenyl halide (Eqn. 20.58). 36. 37 jhe relative position of the activating group to the departing halide has little effect on the amount of halogen lost. 2 d36... 

Alkylations and arylations Simple alkylations of [ " C]cyanoacetates are of lesser importance than of dialkyl [ C]malonates because the products, a-i Clcyanoalkanoic esters, are usually more readily available via [ " C]cyano-dehalogenation of a-bromo esters, or by alkoxy-carbonylation of alkyl [ " C]nitriles with chloroformates or dialkylcarbonates (analogous to Routes C and D in Figure 7.33). Both of these alternatives avoid problems... 

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