Reduction of -camphorquinone

Metal-ammonia reduction of bicyclo[2,2,l]heptanones has been examined by Coulombeau and Rassat, who point out that the conformationally more stable forms of substituted alcohols are the exo-isomers in the case of norbornan-2-ol and the 1-methyl homologue, but the endo-isomers in the case of borneol (1,7,7-trimethyl) and fenchol (1,3,3-trimethyl). The same authors have also examined the reduction of camphorquinone [2,3-dioxo-bornane, (249)] with... 

The ewrfo-configuration of the hydroxyketones 82 and 83 formed from camphorquinone has been unequivocally established 15> and shown to be related to configurations of the aldehyde adducts. This stereochemical result requires attack from the normally more hindered side of the molecule. As discussed earlier (cf. Table 4) m-methoxyacetophenone sensitized the reduction of camphorquinone in 2-propanol, and benzo-... 

The reduction of cyclohexane-l,2-dione 38 (Figure 21.12) gave racemic trans-cyclohexane-l,2-diol 39 [179, 180]. From the reduction of camphorquinone 40, a 63% yield [96] of cxo-2-hydroxy camphor 41 and 3-hydroxy camphor 42 was obtained. In addition, the reduction of substituted acenaphthenequinones afforded the corresponding 2-hydroxyacenaphthenones in 24-48% yields with 10-93% ee [181]. The Wieland-Miescher ketone has also been reduced with high enantioselectivity [182]. 

The enzyme catalyzing the reduction of ketopantolactone to D-pantolactone was isolated in a crystalline form from the cells of Candida parapsilosis and characterized in some detail [106] (see Tables 4 and 5). It is a novel NADPH-dependent carbonyl reductase with a molecular mass of about 40,000. In addition to the reduction of ketopantolactone, the enzyme catalyzes those of a variety of cyclic diketones, including derivatives of ketopantolactone, isatin, camphorquinone and so on, to give the corresponding (R)-alcohols [106, 107], The enzyme was termed conjugated polyketone reductase , since the enzyme catalyzes only the reduction of conjugated polyketones as follows. 

Calcium D-galactonate, I, 70 Calcium D-gluconate, III, 141, 142, 149, 152, 155, 156, 161 IV, 331 Calcium hypochlorite, III, 165 Calcium 2-keto-D-gIuconate, III, 148, 155 Calcium 5-keto-D-gluconate, III, 156 Calcium lactobionate, calcium bromide double salt, III, 155 Calcium Ievulinate, IV, 311 Calcium maltobionate, III, 161 Calcium D-mannonate, III, 152 Calcium pectate, I, 334 Calcium D-rhamnonate, III, 144 Calcium salts, in preparation of aldonic acids with NaCN, I, 23 Calcium vicianobionate, III, 154 Calcium D-xylonate, III, 155 Camphor, optically active, formed from inactive (racemic) camphor carboxylic acid in the presence of quinine, quinidine or nicotine, V, 53 Camphor carboxylic acid. See Camphor. Camphor, 3-hydroxy-, IV, 89 Camphorquinone, phytochemical reduction of, IV, 89... 

Preparation of the Auxiliary. A synthesis of the (1/ ) auxiliary has been reported starting from (-i-)-camphor (eq 1). Zinc reduction of the intermediate imine (2) followed by sulfonylation and ketone reduction with Ca(B 114)2 afforded the cis.endo product in 70-75% overall yield from camphorquinone (1). 

Two sterically hindered /V-sulfonylated aminobomeols 42 were prepared from camphorquinone 11 and used after esterification for the formation of enolates which are alkylated or oxidized diastereoselectively (Sections D.1.1.1.3.2., D. 1.5.2.1., D. 1.5.2.3. and D.4.I.). The synthesis of these auxiliaries involves the reaction of camphorquinone 11 with 3,5-dimethylaniline to give the mono-imine by reaction with the sterically less hindered carbonyl group, followed by reduction with boranate and reaction with benzenesulfonyl chloride to give the exo.exo-product. or initial reduction with zinc/potassium hydroxide, then sulfonylation, and finally reduction with boranate to give the endo,endo-isomer21. 

Camphorquinone (12), which has been studied in several solvents, gives typical hydrogen atom abstraction reactions. It undergoes photoreduction in isopropyl alcohol39,71,72 and forms mixtures of solvent addition and reduction products when irradiated in methanol,39,71 aldehydes,73 and xylene.23 No transformation is observed in benzene or carbon tetrachloride.74... 

Reduction is observed principally with those a-diketones which do not form diketopinacols (63) including camphorquinone is,97.99) tetra-methyltetralindione 60>, and 2,2,5,5-tetramethyltetrahydrofuran-3,4-dione 15>. A low yield of benzoin was reported 37> in the reaction of cyclohexane solutions of benzil. The isomeric diols obtained from camphorquinone had the endo configuration 15,97.99). 

Alcohols are usually oxidized to aldehydes or ketones in these reactions cholestanone has been isolated 128> from reaction of cholestanol and phenanthrenequinone in benzene solution. Two cases have been reported, both involving reactions in methanol, where the intermediate hydroxymethyl radical coupled (in part) with semidione radical. Thus, the 1,2-adducts (34%) 84 and 55 were obtained "> with camphorquinone at 2537 A in addition to 82 and83 (66%). 1,2-Adduct (35%) predominated 6°) over reduction product (18%) in reaction of 73 in methanol. This reaction led to a very complex mixture of products, some or all of which may reflect reactions of the monohemiketal since light filtered through Pyrex was used and decolorization of the dione was observed in methanol solution. 

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