Chloro ketones reduction with zinc

Halogen substituents in a "-haloketones are easily removed even by zinc dust, because of the greater tendency of the halogen to ionisation. The reduction may be represented by a mechanism like that for acetoxy ketones, the ease of removal of halogens following their usual order of reactivity F < Cl < Br < I. In one case the intermediacy of an enolate anion was revealed by direct isolation of an enol acetate aa-chloro-Sa-cholestan 3 One was dechlorinated with zinc in acetic anhydride to give 3-acetoxycholest-2 ene [ 112]. 

Michael addition of the (S nitroester 95 to the unsaturated ketone 96 gave a mixture of 97 and the (22S)-isomer (207, 208). Sodium borohydride reduction of 97 in an acidic medium afforded the nitrodiol 98 in excellent yield. Reduction of the nitro group and subsequent lactam formation (99) proceeded smoothly when the nitrodiol 96 was refluxed with zinc and acetic acid. Further reduction of the amide 99 with LAH yielded the piperidine 100, which was converted into its iV-chloro derivative. Treatment of this compound with sodium methoxide effected dehydrochlorination which was... 

TrimethylsUyl enol ethers. It is relatively easy to obtain trimethylsilyl enol ethers formed under kinetic control from unsymmetrical ketones in high yields by use of LDA as ba (3, 310 311). However, the more highly substituted enol ethers formed by thermodynamic control have not been available as readily. A new method that leads to the more highly substituted ether uncontaminated with the less highly substituted ether is reduction of n-halo-a-substituted ketones with activated zinc (I, 1276) in ether TMIiDA followed by addition of chloro-trimcthylsilanc in ether. The starting materials can Ire prepared by ehlorination of the, < dkvl ketf>iie with stdliiryl chloride. ... 

Titanium(iii) chloride and HCl provide a means of reduction of a,a-dibromo-ketones to the corresponding a-chloro-compounds [equation (50)]. ° a,a -Dibromo-ketones are reduced to a-acetoxy-ketones by ultrasonically dispersed mercury in acetic acid. A wide variety of dienes react with a,a -dibromo-ketones in the presence of a zinc-silver couple or an iron carbonyP in the [3 + 4 - 7] sense to give cyclohept-4-enones [equation (51)]. 

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