Allyl acetates hydrogenolysis

Hydrogenolysis of allylic acetates.1 This reaction can be effected in high yield by hydrogenolysis catalyzed by Pd(OH)2 on carbon and with cyclohexene as the... 

Hydrogenolysis of allylic acetates. Allylic acetates (or carbonates or chlorides) are converted into terminal alkenes by ammonium formate using a Pd(ll) catalyst com-plexed with a trialkylphosphine, particularly P(n-Bu),. 

While in propargylic systems a vinylogous reduction is the normal reactivity, in allylic systems a double bond shift on reduction is realized more generally only when terminal alkenes are produced. Especially Interesting in this respect is the Pd-catalyzed hydrogenolysis of allylic acetates (X = OAc) with ammonium formate (equation 45). ... 

Hydrogenolysis of allylic formates. The Pd(0) catalyst generated from Pd(OAc)2 and Bu2P effects hydrogenolysis of allylic acetates or carbonates with ammonium formate to afford 1-alkenes. Allylic formates are also converted to 1-alkcncs by this Pd(0) catalyst without use of ammonium formate. 

Hydrogenolysis can occur using dissolving metal conditions, and is particularly useful for the cleavage of O-benzyl and N-benzyl derivatives. It is widely used as a useful alternative to catalytic hydrogenation. Treatment with sodium in ammonia cleaves the O-benzyl group, as in the conversion of 491 to 492 (in 90% yield), in Mulzer s synthesis of hastanecine. l Note that the byproduct is toluene. It is also possible to cleave other reactive C—O (or C—N) bonds. Allylic acetates, for example, are cleaved to the hydrocarbon, as shown by the reaction of 493 with lithium and ammonia to give an 81% yield of 494. ... 

Hydrogenolysis of allyl acetate with [PdCl2L2] (L = l, 6, 7) catalyst proceeded smoothly in heptane/aqueous sodium formate mixtures at 80 °C [57]. The catalyst, formed in situ from [Pd(OAc)2 and TPPTS, could be used for the selective removal of allylic protecting groups such closely related protecting groups as dimethyl-allylcarbamates and allyloxycarbonates could also be distinguished [58, 59]. 

The 1,5-diketone 21 is prepared by 3-butenylation of ketones to give 20 via Pd-catalyzed hydrogenolysis of the allylic acetate 19, followed by Pd-catalyzed oxidation, and is used for annulation to form the cyclohexenone 22 [19]. In this method, the 3-butenyl group is a masked methyl vinyl ketone. Preparation of the 1,7-diketone 24 was performed by oxidation of 23, and applied to the synthesis of dysidiolide (25) [23]. 

In 1973, Hey and Arpe first reported Pd-catalyzed hydrogenolysis of aUyUc esters, phenyl ether, and amine using formic acid as a hydride source. In their attempt to prepare allylic formates from various allylic acetates by Pd-catalyzed transesterification, they obtained a mixture of alkenes instead of the expected allylic formatesf (Scheme 2). 

The ene oxide 266 was prepared from 5-methyl-(2Z)-hexene-l-ol first by Sharpless epoxidation followed by Swem oxidation the aldehyde was submitted to Wittig reaction and the resulting alcohol was esterified to lead to ene oxide 266. Pd-catalyzed cyclization in the presence of Pd2(tba)3-CHCl3 and DPPE in THF at 25 °C gave the lactone 267 with high regio- and stereoselectivities. Introduction of the butenyl chain of the lactone was successful by Pd-catalyzed alkylation with the appropriate aUylic carbonate. The allylic substitution proceeded stereoselectively in 51% yield. The Pd-catalyzed hydrogenolysis of allylic acetate with formic acid and triethylamine afforded the lactone 268 (Scheme 62). 

Palladium-catalysed hydrogenolysis of allylic acetates and allylic phenyl ethers with ammonium formate provides a convenient method of preparation of 2-olefins [equation (5)]. The preferred catalyst is the readily available complex... 

The homogenous catalyst tris(triphenylphosphine)chlororhodium was chosen for hydrogenation to avoid the possibility of hydrogenolysis of the allylic acetate. 

Vinylogs of benzylic alcohols, e.g. cinnamyl alcohol, undergo easy saturation of the double bond by catalytic hydrogenation over platinum, rhodium-platinum and palladium oxides [39] or by reduction with lithium aluminum hydride [609]. In the presence of acids, catalytic hydrogenolysis of the allylic hydroxyl takes place, especially over platinum oxide in acetic acid and hydrochloric acid [39]. 

Refluxing with zinc in ethanol reduced a-bromocinnamic acid to cinnamic acid in 80% yield [997]. Allylic chlorines in y,y,y-trichlorocrotonic acid were partly or completely hydrogenolyzed by zinc and sodium amalgam [5/9]. Hydrogenolysis of allylic bromine in oc, -unsaturated esters with zinc in acetic acid gave predominantly, y-unsaturated esters in 65-97% yields [998]. 

The hydrogenolysis of allylic ether and acetate (235 236, R=alkyl or COCHj) should also take place more easily when the compound can adopt a conformation in which the OR group can become parallel to the u orbital of the double bond (69). The same stereochemical requirement must also be necessary in the hydrogenolysis of a substituent in a benzylic position (70). 

One protecting method for ketones and aldehydes is the formation of oximes, but sometimes further protection of the oximes is required. For this purpose, the oximes can be protected as the allyl ethers 335, which are deprotected by the Pd-catalysed hydrogenolysis with HCO2H Et3N in boiling dioxane under mild conditions without attacking the acetal group in 335 [153],... 

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