Hydrogenolysis aryl substituted

Extreme differences between 5% palladium-on-carbon and platinum oxide were found on reduction of the 5-aryl substituted oxazole 14. Over palladium, 15 was formed in quantitative yield by hydrogenolysis of the benzyl hydroxyl, whereas over Pt, scission of the oxazole occurred to give 13 quantitatively (48). Hydrogenation of 15 over platinum oxide gave the phenethylamide 16. 

Cyclopropanes can be cleaved by catalytic hydrogenolysis. Among the catalysts used have been Ni, Pd, and Pt. The reaction can often be run under mild condi-tions." ° Certain cyclopropane rings, especially cyclopropyl ketones and aryl-substituted cyclopropanes," can be reductively cleaved by an alkali metal (generally Na or Li) in liquid anunonia." Similar reduction has been accomplished photo-chemically in the presence of LiC104." ... 

The hydrogenolysis of l-azabicyclo[3.1.0]hexane (68) took place with the breaking of both C-N bonds giving 2-methylpyrrolidine and piperidine in a 2 1 ratio (Eqn. 20.49)." With aryl substituted aziridines the C-N bond adjacent to the aromatic ring is preferentially hydrogenolized (Eqn. 20.50). ... 

Transition metal-catalyzed cross-coupling reactions of halogenopyrazines is an efficient synthetic method for alkyl-, alkenyl-, and alkynylpyrazines (Section 6.03.5.4.2). Palladium and nickel complexes are particularly effective as catalysts in this reaction. The Wittig reaction of halogenomethyl-pyrazines likewise leads to the formation of alkenylpyrazines (Section 6.03.8.1). Dehalogenation of halogeno pyrazines is a very practical synthetic method for alkyl- or aryl-substituted pyrazines. For example, phenylpyrazine has been prepared by catalytic hydrogenolysis of the 2-chloro-3-phenyl compound in the presence of triethylamine. This product is also obtained by decarboxylation of... 

Palladium-catalyzed aminations of aryl halides is now a well-documented process [86-88], Heo et al. showed that amino-substituted 2-pyridones 54 and 55 can be prepared in a two-step procedure via a microwave-assisted Buchwald-Hartwig amination reaction of 5- or 6-bromo-2-benzyloxypyri-dines 50 and 51 followed by a hydrogenolysis of the benzyl ether 52 and 53, as outlined in Fig. 9 [89]. The actual microwave-assisted Buchwald-Hartwig coupling was not performed directly at the 2-pyridone scaffold, but instead at the intermediate pyridine. Initially, the reaction was performed at 150 °C for 10 min with Pd2(dba)3 as the palladium source, which provided both the desired amino-pyridines (65% yield) as well as the debrominated pyridine. After improving the conditions, the best temperature and time to use proved... 

As seen in the retro-synthetic Scheme 5.3, intermediate 15 is useful for both routes. The choice of benzyl protection group was made based on the robust stability of benzyl phenol ethers toward most reactions and several possible avenues to remove it, although it was reported from Medicinal Chemistry that benzyl group removal via hydrogenolysis posed challenges in this compound. The choice of iodide substitution was born out of the known high reactivity of iodides in the Ullmann-type coupling reaction with alcohols and the robust stability of aryl iodides in many other common reactions. 

This chapter surveys the reduction of saturated alkyl halides to alkanes. Reductive -eliminations of vicinal dihalides to alkenes are also described briefly. Reduction of vinyl and aryl halides is covered in this volume. Chapter 4.5 hydrogenolysis of allyl and benzyl halides is covered in this volume. Chapter 4.7, and reduction of a-halo-substituted carbonyl compounds CX—CO to carbonyl compounds CH—CO is covered in this volume. Chapter 4.8. 

The hydrogenolysis of arylpalladium(II) species is a widely used reaction for the dehydrohalogenation of arenes. In combination with the Catellani reaction sequence, hydrogenolysis of a complex of type 36 leads to a meto-substituted arene product. In Catellani s stoichiometric investigations of the orf/io-alkylation [43] and orf/to-arylation [88, 89] of the PNP dimer, H2 or NaBH4 were used for reduction of the resultant o,o -disubstituted arylpalladium(II) species (Scheme 38). 

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. 

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