Aryl chlorides hydrogenolysis

Hydrogenolysis of aryl and alkenyl halides and triflates proceeds by the treatment with various hydride sources. The reaction can be explained by the transmetallation with hydride to form palladium hydride, which undergoes reductive elimination. Several boro hydrides are used for this purpose[680], Deuteration of aromatic rings is possible by the reaction of aryl chlorides with NaBD4681]. 

An interesting case is the hydrogenolysis of aryl chlorides, bromides and iodides in respective yields of 72%, 72% and 82% on irradiation in isopropyl alcohol [310]. 

Examples of hydrogenolysis of aryl chlorides by lithium aluminum hydride are rare. Chlorobenzene is reduced to benzene only in a low yield, but chloronaphthalene gives a good yield of naphthalene with lithium aluminum hydride in the presence of either di-r-butyl peroxide or titanium tetrachloride (equation 51 ). ... 

Hydrogenolysis of aryl chlorides can also be achieved by treatment with triethylsilane in the presence of palladium, and by reduction with isopropyl alcohol under UV irradiation (equation 53). ... 

The hydrogenolysis of aryl halides proceeds more readily than the cleavage of alkyl-halogen bonds. Aryl chlorides are rather stable to hydrogenolysis in neutral medium and bromides are dehalogenated only to a moderate extent 24,132 but iodides are readily lost. Aryl fluorides, however, are hydrogenolyzed only under... 

Under ligandless conditions PdCl2 catalyzed the hydrogenolysis of several 4-substituted aryl chlorides in alkaline aqueous solutions using NaH2P02 as reductant (Scheme 3.40) [275]. In case of certain ortho-substituted substrates, such as 2-chlorophenolate and 2-chloroaniline, strong chelation in the intermediate palladacycle completely inhibited the reaction. On the other hand, in case of 2-chlorobenzoic acid addition of iodide led to 86 % yield of benzoic acid. 

Although transfer hydrogenolysis conditions can be used to remove a 1 -chloride such as 235,modification of the reaction conditions also allowed the selective removal of the aryl chloride in 237 while leaving the alkyl chloride untouched (Scheme 72). 

Water-soluble aryl chlorides undergo hydrogenolysis in aqueous alkaline media in the presence of PdCl2 with NaH2P02 as hydrogen source [84] ... 

Aiyl esters, prepared from the phenol and an acid chloride or anhydride in the presence of base, are readily cleaved by saponification. In general they are more readily cleaved than the related esters of alcohols, thus allowing selective removal of phenolic esters. 9-Fluorenecarboxylates and 9-xanthenecarboxylates are also cleaved by photolysis. To permit selective removal, a number of carbonate esters have been investigated aryl benzyl carbonates can be cleaved by hydrogenolysis aryl 2,2,2-trichloroethyl carbonates, by Zn/THF-H20. 

Hydrogenolysis Aryf Chlorides 4.5.2.4 Hydrogenolysis Aryl Bromides... 

Because of the different rates of hydrogenolysis, aryl halides containing different halogens can be reduced selectively. 1 -Bromo-2-chlorobenzene is reduced to chlorobenzene in 96% yield on treatment for 2 h at room temperature with a complex reducing agent prepared from nickel(II) chloride, sodium hydride and t-pentyl alcohol. l-Bromo-4-chlorobenzene is converted to chlorobenzene on treatment with... 

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