Hydrogen transfer reagents

Two years later. Piers et al. reported an improved synthesis of isogranulatimide (375) starting from didemnimide A (373). Heating of a solution of 373 in nitrobenzene containing palladium black as the hydrogen transfer reagent at... 

All the examined alcohols were active as hydrogen transfer reagents both towards the olefinic and the carbonylic double bond in a wide range of temperatures (60°-140°C). 

Durst and Sharma [86] have reported the stereospecific synthesis of 3-spiro-epoxyazetidin-2-ones 55 (Scheme 14). The oxidation of the diastereoisomers of compound 52 with PCC provided a single acetyl compound 3-acetyl-3-benzyloxy-azetidin-2-one 53. Nonchelation controlled L-Selectride reduction of 53 gave the isomerically pure 3-hydroxyethylazetidin-2-one as the sole reduced product, which was further converted to tosylate 54 using NaH/tosylimidazole. The debenzylation-oxirane formation sequence was conveniently performed as a single pot operation with ammonium formate, 5% Pd/C in refluxing methanol as the hydrogen transfer reagent combination. 

Use of ammonium formate as a catalytic hydrogen-transfer reagent has been reviewed.2... 

The reaction is thermodynamically controlled. A cyanohydrin is added, in practice, to the anion /i as a hydrogen transfer reagent (Equation (44)),... 

Dihydroanthracene has been used as one of the hydrogen transfer reagents in a series of homolytic hydrogen transfer reactions by Braude, Jackman, and Linstead and as a hydrogen donor for the hydrogenation of thiyl radicals to form thiols. ... 

While hydrogenation using metal hydrides and other hydrogen transfer reagents offers a feasible method for laboratory experimentations, activation of molecular hydrogen with metal or metal organic catalysts is broadly employed in industrial hydrogenation processes. 

In 2005, Rueping et al. reported that chiral phosphoric acids function as an efficient catalyst for the enantioselective reduction of ketimines (Scheme 3.40a 1) [87]. A variety of aryl methyl ketimines were reduced to the corresponding amines in optically active forms using Hantzsch ester as the hydrogenation transfer reagent (HEH) [88]. Subsequently, List and coworkers improved the catalytic efficiency and enantioselectivity by thorough optimization of the substituents (G) that were introduced to the phosphoric acid catalyst (Scheme 3.40a 2) [89]. Almost simulta neously, MacMillan and coworkers successfully developed the enantioselective... 

Ketones can be reduced to secondary alcohols by H and a catalyst or a complex metal hydride or by hydrogen transfer reagents. Deoxygenation with a strong base at 150°C (302°F) can form olefin. Ketones react with thiols to form thioacetals. Reaction with anhydrous hydrazine may be explosive. 

TABLE 2. Common Hydrogen-Transfer Reagents in Free Radical Reactions... 

Other Hydrogen-Transfer Reagents Group III Hydride-Donor Reagents... 

Hydrogen-transfer Reagent in Radical Reactions. Thiols, in particular tertiary mercaptans such as tert-butanethiol and triethylmethanethiol, have been widely used in radical reactions to trap radical intermediates by hydrogen atom transfer. ferf-Dodecanethiol is a vahd substitute for those mercaptans, since it is cheap, relatively odorless compared to the other alkanethiols, and generally equally efficient with respect to the hydrogen donor properties. 

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