Norbornanol, oxidation

Using two types of specially synthesized rhodium-complexes (12a/12b), pyruvate is chemically hydrogenated to produce racemic lactate. Within the mixture, both a d- and L-specific lactate dehydrogenase (d-/l-LDH) are co-immobilized, which oxidize the lactate back to pyruvate while reducing NAD+ to NADH (Scheme 43.4). The reduced cofactor is then used by the producing enzyme (ADH from horse liver, HL-ADH), to reduce a ketone to an alcohol. Two examples have been examined. The first example is the reduction of cyclohexanone to cyclohexanol, which proceeded to 100% conversion after 8 days, resulting in total TONs (TTNs) of 1500 for the Rh-complexes 12 and 50 for NAD. The second example concerns the reduction of ( )-2-norbornanone to 72% endo-norbor-nanol (38% ee) and 28% exo-norbornanol (>99% ee), which was also completed in 8 days, and resulted in the same TTNs as for the first case. 

When norbornene is treated with trichlorosilane in this manner, quantitative yield of evo-2-trichlorosilylnorbornane is obtained, and (lS,2S,4R)-exo-2-norbornanol can be obtained in 96% ee upon hydrogen peroxide oxidation.28 This reaction can be extended to other olefinic substrates such as 2,5-... 

Interestingly, when solvents possessing a lower polarity than benzene—such as heptane—are employed, a substantial acceleration of the oxidation can be observed. Thus, endo-2-norbornanol (70) is oxidized 11 times faster in heptane than in benzene.5 In fact, even weak ligands such as alkenes can produce a substantial slowing of the oxidation. For example, endo-2-norbornenol (71) reacts 50 times slower than endo-2-norbornanol (70) with Fetizon s reagent.5... 

The same method also results in quantitative yields from the oxidation of 1,2-diphenylethanol and in much improved yields from oxidation of 7-norbornanol. ... 

The hydrosilylation-oxidation of simple unfunctionalized alkenes has not been widely used for the diastereoselective preparation of alcohols, probably because it would not in general be expected to give very different results to hydroboration oxidation. One example which has been reported is the exo-selective hydrosilylation of norbornene (1) with trichlorosilane and hexachloroplatinic acid6, followed by oxidation to c.vo-norbornanol (2)1. 

Recently, much better results have been obtained using the palladium catalyst D [with ( + )-(/ )-MOP], Hydrosilylation of norbomene with trichlorosilane in the presence of this catalyst gives a quantitative yield of e.vo-2-trichlorosilylbornane which upon oxidation produces (l.S .2.S.4f )- .w-2-norbornanol (25) with 96% ee30. 

Gas chromatographic analysis shows this material to have a purity of about 96%. Besides a small amount of water (up to 0.5%) there are two minor impurities. Neither 2-cx< -norbornyl formate nor 2-ew-norbornanol is present, however. Oxidation of 2-ep o-norbornanol with chromic acid, under a variety of conditions, gives 2-norbornanone contaminated with some starting material. 

Oxidative cleavage of bicyclic alcohols. Oxidation of either exo- or endo-norbornanol (1) with 2 equiv. of ceric ammonium nitrate in 50% aqueous acetonitrile at 50° gives three products of oxidative cleavage, 3- and 4-cyclopentene-acetaldehydes (2) and (3) and 3-nitratocyclopentaneacetaldehyde (4).3 Oxidation... 

Long (17) observed that ozonation of norbornane (bicyclo-2,2,I-hep-tane) in CCI4 at 0°C. gives only gaco-2-norbornanol and 2-norbornanone. We have confirmed this result using cyclohexane as solvent and gas chromatography for analysis less than 2% of any other alcohol or ketone is formed. Endo-2-norbornanol could not have been formed initially and then rapidly oxidized to 2-norbornanone. In a control experiment 6 mg. of endo-2-norbornanol were added to 1.7 grams norbornane in 8 ml. of cyclohexane and ozonized for 95 minutes. Then, 75% of the endo-2-norbornanol was oxidized. Thus, it is oxidized under the reaction condi-... 

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