Propargyl compounds hydrogenolysis

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

Allenes 169 and alkynes 170 are prepared by hydrogenolysis of propargyl compounds with several hydrides. Triethylammonium formate is used most conveniently under mild conditions [45]. Chromium tricarbonyl-complexed phenylallene 172 was prepared from the carbonate 171 [46]. The alkyne 174 was obtained selectively from the propargyl formate 173 having an amino group [47]. 

Pd-catalyzed hydrogenolysis of allylic compounds with formates is an efficient and mild method. The hydride generated from the palladium formate attacks the more substimted side of the allylic system to give less substituted olefins in contrast to the case with other hydride sources. Pd-catalyzed hydrogenolysis of propargylic compounds affords either aUenes or alkynes depending on the structure of the propargylic compounds. 

Hydrogenolysis of Allylic and Propargylic Compounds with Various Hydrides. 

Hydrogenation of the 1-propargyl and 1-allyl derivatives of 63 (R = H) over Pd/CaC03 or Pd/C gave the 1-propyl compound,103 273 whereas 2-propargyloxy-4-oxo-4A/-pyrido[l,2- ]pyrimidine yielded the 2-propyloxy compound.273 Catalytic hydrogenation of the 2-alkoxy- and 2-aralkoxy-4-oxo-4A/-pyrido[l,2- ]pyrimidines was accompanied by the hydrogenolysis of the substituents in position 2.112,114... 

Acetylenic carbinols, which are manufactured from aldehydes or ketones and acetylenes, can be partially hydrogenated, with the exception of propargyl alcohol itself. Hydrogenolysis is a minor side reaction unless the hydrogenation is completed to the alkane. Nickel boride (PI or P2) catalysts achieve the saturation of propargyl and allylic compounds in the presence of double bonds without hydrogenolysis, such as in 2 an intermediate in the total synthesis of the sesquiterpene sesquicarene ... 

Catalytic hydrogenation of alkynes takes place in a stepwise manner, and both the alkene and the alkane can he isolated. Complete reduction of alkynes to the saturated compound is easily accomplished over platinum, palladium or Raney nickel. A complication which sometimes arises, particularly with platinum catalysts, is the hydrogenolysis of hydroxyl groups a- to the alkyne (propargylic hydroxyl groups) (7.15). 

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