Transfer hydrogenation with formate

Opening to the -rr-allyl complex 9.214, which was reduced by hydride transfer from formate. Unlike most other nucleophiles (see Schemes 9.32 and 9.34), formate transfers hydrogen with retention, giving the required stereochemistry for the natural product. Completion of the synthesis included a nickel-catalysed Kumada coupling to convert the ketone, via an enol phosphate 9.216, into a methyl group and a McMurry reaction to close the seven-membered ring. 

One very fast and reliable method for the reduction of double bonds is that of transfer hydrogenation with diimine (Scheme 20.30). Under the influence of traces of copper ion and oxygen from air, hydrazine is rapidly transformed into diimine. This compound is able to hydrogenate double bonds with great success under the formation of nitrogen [120],... 

The rapid microwave-assisted deprotection of N-benzyl carbamate (Cbz) and AT-benzyl (Bn) derivatives in solution as well as on solid support was reported by Daga et al.26 Within this report, amino groups protected as benzyl carbamates or with simple benzyl groups could be deprotected in a few minutes by microwave-assisted catalytic transfer hydrogenation with palladium charcoal in isopropanol, employing ammonium formate as the hydrogen donor (Scheme 7.6). Both MeO-PEG and PS Wang-resin were used as soluble and solid supports, respectively, in these reactions. 

Catalytic transfer hydrogenation with alcohols for the CLA formation 384... 

CATALYTIC TRANSFER HYDROGENATION WITH ALCOHOLS FOR THE CLA FORMATION... 

Petrini and co-workers used the bis(methoxymethyl)-protected nitrone 150, also derived frern L-tartrate, as an electrophile rather tfaiui as a 1,3-dipole (Scheme 21, top line) (89). In their key step, reaction with 4-ben loxybutylmagnesium bromide gave the cyclic hydroxylamine 151 in 82% yield (de 90%). Transfer hydrogenation with ammonium formate and a palladium catalyst cleaved both the hydroxylamine and the benzyl ether, affording the aminoalcohol 152. Cyclization via the corresponding primary chloride created the protected indolizidine 153, acidic hydrolysis of t ch completed this short synthesis of ( + )-132 in 16%... 

The reductive animation of 3-oxo-l,2.3.4-tetrahydrocarbazole with (S)-phenylethylamine and sodium borohydride leads to (37 )-3-[(l.S )-phenylethylamino]-l,2,3,4-tetrahydrocarbazole in 39.7% yield. The cleavage of the phenylethyl group is accomplished by a transfer hydrogenation, with ammonium formate as a hydrogen donor and palladium on charcoal as a catalyst, to give the enantiomerically pure (3/ )-3-amino-l,2,3,4-tetrahydrocarbazole23. 

ZrC>2 promotes transfer hydrogenation. 1,3-Butadiene undergoes transfer hydrogenation with 1,3-cyclohexadiene to form 1-butene over Zr02[17j. The selective formation of 1-butene is in contrast to the hydrogenation with H2 where trans-2-butene is selectively formed. 

Benzyl trichloracetimidate (48) is a new reagent for acid-catalysed benzylation of alcohols in the presence of trifluoromethanesulphonic acid, and benzyl p-toluenesulphonate-potassium carbonate has been recommended as abenzylat-ing system for phenols, especially in cases where benzyl chloride-potassium carbonate gives C-alkylated impurities.Facile removal of benzyl ether protecting groups has been achieved by catalytic transfer hydrogenation with Pd(OH)2 on carbon and cyclohexene as hydrogen-donor. A new procedure for O-tritylation by treatment of an alcohol trimethylsilyl ether with trityl trimethylsilyl ether is shown in equation (6). The synthesis and characterization has been completed of 4-dimethylamino-N-triphenylmethylpyridinium chloride (49)," a postulated intermediate in the formation of trityl ethers from alcohols... 

Sanz, S. Azua, A. Peiis, E. (il6-arene)Ru(bis-NHC) Complexes for the Reduction of COj to Formate with Hydrogen and by Transfer Hydrogenation with iPrOH. Dalton Trans. 2010, 39, 6339-6343. 

The mechanism of the C02 transfer reaction with acetyl CoA to give mal-onyl CoA is thought to involve C02 as the reactive species. One proposal is that loss of C02 is favored by hydrogen-bond formation between the A -carboxy-biotin carbonyl group and a nearby acidic site in the enzyme. Simultaneous deprotonation of acetyl CoA by a basic site in the enzyme gives a thioester eno-late ion that can react with C02 as it is formed (Figure 29.6). 

The catalytic alcohol racemization with diruthenium catalyst 1 is based on the reversible transfer hydrogenation mechanism. Meanwhile, the problem of ketone formation in the DKR of secondary alcohols with 1 was identified due to the liberation of molecular hydrogen. Then, we envisioned a novel asymmetric reductive acetylation of ketones to circumvent the problem of ketone formation (Scheme 6). A key factor of this process was the selection of hydrogen donors compatible with the DKR conditions. 2,6-Dimethyl-4-heptanol, which cannot be acylated by lipases, was chosen as a proper hydrogen donor. Asymmetric reductive acetylation of ketones was also possible under 1 atm hydrogen in ethyl acetate, which acted as acyl donor and solvent. Ethanol formation from ethyl acetate did not cause critical problem, and various ketones were successfully transformed into the corresponding chiral acetates (Table 17). However, reaction time (96 h) was unsatisfactory. 

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