Catalytic transfer hydrogenolysis

In spite of the successful application of catalytic transfer hydrogenolysis in the case of benzylic compounds, this method is not suitable for the cleavage of the allylic C-O bonds. 

N-Substituted pyrrolidines were subjected to catalytic transfer hydrogenolysis affording pyrrolidines, but the yields were low. However, when di-tert-butyl dicarbonate was added to the N-substituted pyrrolidines before catalytic hydrogenolysis, the N-Boc derivatives were all formed in good yield (Scheme... 

Catalytic hydrogenation of azo compounds over Pt or Ra-Ni often leads to hydrogenolysis. 551 Catalytic transfer hydrogenolysis using cyclohexene and Pd is also used for the conversion of azobenzenes to anilines.552... 

FIGURE 7.22 A one-pot synthesis of a protected tripeptide in tetrahydrofuran using IV-alkoxycarbonylamino-acid IV-carboxyanhydrides.77 The amino group of the second residue is liberated by catalytic transfer hydrogenolysis (see Section 6.21). 

M. C. Cruzado and M. Martin-Lomas, The heterogeneous, catalytic, transfer hydrogenolysis of tri-O-benzyl derivatives of 1,6-anhydro-p-rvhexopyraiioses, Carbohydr. Res. 770 249 (1987). 

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. 

Catalytic transfer hydrogenolysis of a BOM ether and benzyloxycarbonyl (Cbz) group using formic acid as the hydrogen source launched the finale to a synthesis of the Tbnicamycin antibiotics [Scheme 4.274].71 Subsequent treatment of the crude amino pentaol 274 2 with 13% formic acid in methanol at 40 °C for 5 h then resulted in methanolysis of the jV-Boc and isopropylidene acetal groups. To complete the sequence, the TBS ether group was deleted with HF to furnish the amino polyol 274.4 in 90% overall yield for the 3-step sequence. 

Cleavage of Merrifield Resins by Catalytic Transfer Hydrogenolysis... 

Removal of halogen from aromatic rings can also be accomplished by various reducing agents, among them BusSnH, " catalytic hydrogenolysis, " catalytic transfer hydrogenolysis, ... 

In numerous applications the presence of acyl protecting groups cannot be tolerated. In these cases Aralkyl protection often provides a viable alternative. For instance, the A -benzyl group proved to be the only reliable choice for amino protection in the racemization-free synthesis of a-amino aldehydes (24) from amino acids (Scheme 15). Its removal is best accomplished by catalytic transfer hydrogenolysis or with sodium in liquid ammonia. ... 

Heterogeneous catalytic transfer hydrogenolysis of C-O bonds in aliphatic and aromatic ethers has been reviewed [90]. As an example, catalytic transfer... 

New methods for cleavage of benzyl ethers have been reported. Catalytic transfer hydrogenolysis using ammonium formate as donor over palladlum-on-charcoal has been found to work better than with formic acid or cyclohexene over palladium catalysts. Trityl ethers were also cleaved but not benzylldene acetals. Ozone (0 /02,... 

Treatment of carbohydrate acetals and dithioacetals with iodine in methanol gives acetal cleavage where the acetal is attached at the anomeric centre, methyl glycosides usually result. Some examples are shown in Scheme 3 Catalytic transfer hydrogenolysis of benzyl-... 

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