Ammonium formate, hydrogenolysi

Ammonium formate hydrogenolysis of 7t-allyl-palladium(II) complexes formed via oxidative addition of Pd(0) to propargylic carbonate esters is a useful method for preparing disubstituted alkynes, as depicted below. This method of deoxygenation avoids the use of expensive and toxic reagents often associated with the free-radical Barton-McCombie deoxygenation. °... 

Formate is an excellent hydride source for the hydrogenolysis of aryl halides[682]. Ammonium or triethylammonium formate[683] and sodium formate are mostly used[684,685]. Dechlorination of the chloroarene 806 is carried out with ammonium formate using Pd charcoal as a catalyst[686]. By the treatment of 2,4,6-trichloroamline with formate, the chlorine atom at the /iiara-position is preferentially removed[687]. The dehalogenation of 2,4-diha-loestrogene is achieved with formic acid, KI, and ascorbic acid[688]. 

In addition to standard catalytic hydrogenolysis, methods for transfer hydrogenolysis using hydrogen donors such as ammonium formate or formic acid with Pd-C catalyst are available.216 The Cbz group also can be removed by a combination of a Lewis acid and a nucleophile for example, boron trifluoride in conjunction with dimethyl sulfide or ethyl sulfide.217... 

Pd/CaC03 is also used for the hydrogenolysis of benzyl-oxygen bonds.152 Hydrogenation and hydrogenolysis of an unsaturated benzyl ether over 5% Pt/ C and Pd(OH)2 gave the saturated and deprotected product.153 In contrast, transfer hydrogenolysis with 1,4-cylohexadiene or ammonium formate failed to provide the product cleanly, rapidly, or dependably. 

Ammonium formate and Pd/C in boiling MeOH were used to remove benzyl ether groups in 1 hour.248 249 Transfer catalytic hydrogenolysis using 10% Pd/C and 25% ammonium formate-THF (1 30) at 25°C was run for 2 hours to remove a benzyl ether group.230 Benzyloxynaphthyl ether was hydrogenolyzed on 10% Pt/C and ammonium formate by refluxing in MeOH for 5 minutes or in THF for 30 min.231... 

The a-carbonyl function of a lactam was removed by transfer hydrogenolysis. Its benzyl ester was dissolved in MeOH under argon ammonium formate and 5% Pd/C were added and the reaction mixture was stirred for 1.5 hours.271,272... 

N,N-Debenzylation was accomplished by Pd/C and HC02NH4.349 Debenzy-lation of an N,N-dibenzyltryptamine derivative was sluggish and incomplete using Pd/C as the catalyst. In contrast, transfer hydrogenolysis using ammonium formate-formic acid in the presence of Pd black efficiently afforded the free tryptamine (27) (Scheme 4.102).350... 

Terminal allenes.1 A synthesis of 1,2-dienes (3) from an aldehyde or a ketone involves addition of ethynylmagnesium bromide followed by reaction of the adduct with methyl chloroformate. The product, a 3-methoxycarbonyloxy-l-alkyne (2), can be reduced to an allene by transfer hydrogenolysis with ammonium formate catalyzed by a zero-valent palladium complex of 1 and a trialkylphosphine. The choice of solvent is also important. Best results are obtained with THF at 20-30° or with DMF at 70°. 

Cyclization was carried out at 1 mM peptide concentration in DMF with bis(2-oxo-3-ox-azolidinyl)phosphinic chloride in the presence of TEA. The cyclic product was isolated by RP-HPLC yield 24%. Deprotection was carried out by hydrogenolysis in MeOH over 10% Pd/C with ammonium formate. 115 The product was isolated by RP-HPLC yield 78%. 

Benzyl alcohol linkers, such as those described in Section 3.1.1.1, can also be cleaved by palladium-catalyzed hydrogenolysis. Carboxylic acids have, for example, been obtained by hydrogenolysis of insoluble benzyl esters with Pd(OAc)2/DMF/H2 [89,161]. Resin-bound benzylic carbamates [162,163] and amides [164] can also be released by treatment with Pd(OAc)2 in DMF in the presence of a hydrogen source, such as 1,4-cyclohexadiene or ammonium formate. These reactions are quite surprising, because they require the formation of metallic palladium within the gelated beads. 

Protection of amines homobenzyloxycarbonyl (hcbo) group.2 In contrast to the Cbo group, the homoCbo group is stable to HBr in HO Ac at 25° and to HC1 in ether. It is also less susceptible to hydrogenolysis, but deblocking can be effected by catalytic transfer hydrogenolysis with a Pd/C catalyst in the presence of ammonium formate. Best results are obtained with a catalyst freshly prepared from Pd(OAc)2. 

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