Hydride compounds allylic hydrogenolysis

The Pd-catalyzed hydrogenolysis of allylic compounds by various hydrides gives alkenes. From terminal allylic compounds, either 1-alkenes or 2-alkenes are formed depending on the hydride sources [360a]. 

The hydrogenation of aromatics has been a topic of interest since Sabatier s first synthesis of cyclohexane from benzene with metallic nickel. The role of Nb and Ta aryloxides as catalysts for this reaction was mentioned earlier. Another system that has been studied in detail comprises allyl and hydride complexes of cobalt, e.g., (i73-C3H5)Co[P(OMe)3]3. Like the Nb and Ta compounds cobalt gives cyclohexane with cis stereoselectivity. The active species is probably the hydride, generated from (allyl)CoL3 on hydrogenolysis, which reacts with arenes in a stepwise manner. 

Palladium-Catalyzed Hydrogenolysis of Allylic and Propargylic Compounds with Various Hydrides. Tsuji, J. Mandai, T. Synthesis 1996,1. 

Besides formic acid, many other reducing agents, such as LiAlH4, borohy-drides, hydrosilanes, and tin hydrides have been used for the hydrogenolysis of allylic compounds [7]. 

In the presence of main group organometallic compounds, ketones are obtained. Carbonylation of allylic ester 382 with alkylzinc reagent afforded the ketone 383 in high yield [149]. Carbonylation of allyl chloride 384 in the presence of tin hydride afforded the -unsaturated aldehyde 385 via hydrogenolysis of acylpalladium intermediate [150]. 

Pd-catalyzed hydrogenolysis of allylic compounds with various hydride sources is important not only for the preparation of alkenes, but also for a deprotection of aUyl-derived protecting group. The latter will be discussed in Sect. V.2.3.2. 

It is well known that allylic compounds undergo facile Pd-catalyzed transformation via formation of 7r-allylpalladium complex as an intermediate, followed by attack of various nucleophiles (Scheme 1). Hydride attack on the 7r-allylpalladium intermediate affords the corresponding alkenes as hydrogenolysis products. ... 

Pd-catalyzed hydrogenolysis. An additional example to show the difference of the regio-selectivity depending on the hydride sources is depicted for allylic nitro compound (Scheme 5). 

Pd-catalyzed hydrogenolysis of allylic compounds with formates is an efficient and mild method. The most important feature of the hydrogenolysis is that the hydride generated from the palladium formate attacks the more substituted side of the allylic system to give less substituted olefins. Various terminal allylic compounds are converted to 1-alkenes. - ... 

Hydrogenolysis of Allylic and Propargylic Compounds with Various Hydrides. 

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