Balancing Lewis Acidity and Carbocation Stability for the Selective Deoxyhalogenation of Aryl Carbonyls and Carbinols

Deoxyhalogenationof aryl aldehydes, ketones, carboxylic acids,and esters has been achieved utilizing an appropriate metal halideLewis acid acting as a carbonyl activator and halogen carrier in combinationwith borane-ammonia as the reductant. Selectivity is accomplishedby matching the stability of the carbocation intermediate with theeffective acidity of the Lewis acid. Substituents and substitutionpatterns significantly influence the requisite solvent/Lewis acidcombination. Logical combinations of these factors have also beenapplied for the regioselective conversion of alcohols to alkyl halides.

Automated summary

Deoxyhalogenation of aryl aldehydes, ketones, carboxylic acids, and esters has been achieved by using a suitable metal halide Lewis acid as a carbonyl activator and halogen carrier, in combination with borane-ammonia as the reductant. Selectivity is achieved by matching the stability of the carbocation intermediate with the effective acidity of the Lewis acid. Substituents and substitution patterns significantly influence the choice of solvent/Lewis acid combination. Logical combinations of these factors have also been applied for the regioselective conversion of alcohols to alkyl halides.