Cyclohexadiene, 1,4-, hydrogen donor

A number of hydrogen donors such as cyclohexene, 1,4-cyclohexadiene, and formic acid have been successfully used in the presence of different heterogeneous Pd catalysts (Scheme 4.53). 

Photolysis of 2-naphthyl thioesters in the presence of a hydrogen donor such as 1,4-cyclohexadiene yields aldehydes (80-100%) no photo-Fries reaction products have been reported [60],... 

Benzene and its homologs can be converted to the corresponding cyclo-hexadienes and cyclohexenes, and even cyclohexanes, by treatment with dissolving metals lithium, sodium, potassium or calcium in liquid ammonia or amines. Conversions are not complete, and the ratio of cyclohexadienes to cyclohexenes depends on the metal used, on the solvent, and on the presence of hydrogen donors (alcohols) added to the ammonia or amine [392, 393, 394]. 

Intramolecular transamidation in (3-lactam enediynes can induce concomitant Bergman type cycloaromatization. For instance, Scheme 67, amine 239, which can be stored as its hydrochloride salt in the freezer, reacts in THF at reflux in the presence of cyclohexadiene as a hydrogen donor to produce only trace amounts of the expanded lactam 240 along with aromatic compound 241 as the major compound [173]. 

Reductive addition to electron-deficient olefins can be also performed by using nontoxic (diacyloxyiodo)arenes (5, Scheme 3.4) [9]. In this case, the photocleavage of an iodo-oxygen bond forms an alkylcarboxyl radical that in turn decarboxylates to yield the desired alkyl radical. As an example, phenyl vinyl sulfones are easily alkylated (e.g., by the addition of adamantane) in good yields, provided that a good hydrogen donor such as 1,4-cyclohexadiene is present in solution. 

When these compounds were treated photochemically with electron-deficient alkenes in the presence of an excess of 1,4-cyclohexadiene, serving as hydrogen donor, reductive addition products were obtained according to the generalized scheme [78] ... 

While cyclohexadiene or y-terpinene (hydrogen donors) gives -30% of the thiophene, alcohols were found to produce thioesters and acetylenes along with a lower yield of thiophene. The major side reaction reported is the oligomerization of the intermediate thiophene diradical. 

Deprotection takes place by catalytic hydrogenation in the presence of palladium under a hydrogen pressure of a few atmospheres. This reforms the hydroxyl groups and toluene is easily separated. Hydrogenolysis by transfer does not require any special equipment. An alcohol solution is heated at reflux with the protected sugar in the presence of palladium over charcoal with, as hydrogen donor, cyclohexene or cyclohexadiene which aromatizes in the reaction. 

BD undergoes over metal oxide catalysts [9]. A characteristic feature of this type of hydrogenation is 1,4-addition of two H atoms, i.e. addition of two H at terminal position of 1,3-BD molecule. 1,2-Addition was found when the hydrogenation was carried out over ZrOz catalyst by using a hydrogen donor molecule, cyclohexadiene, instead of Hz [9]. Unlike to the hydrogenation by Hz over oxide catalysts, Si-H added to the 1,2-position of 1,3-BD to yield (1) and no product from... 

In addition, hydrogen transfers occur in the 1,3-cyclohexadiene system to yield the 7t-arene-Fe complexes, (tj -C6Hg)Fe [P(OCH3)3]2 and (t -C6H6)Fe(f " -l,3-C6H8). Cobalt atoms with butadiene, in the presence of a hydrogen donor, yield a (diene)2-Co-H... 

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