Anti Hydroxylations catalyst

Transition metal catalysts not only increase the reaction rate but may also affect the outcome of the oxidation, especially the stereochemistry of the products. Whereas hydrogen peroxide alone in acetonitrile oxidizes alkenes to epoxides [729], osmic acid catalyzes syn hydroxylation [736], and tungstic acid catalyzes anti hydroxylation [737]. The most frequently used catalysts are titanium trichloride [732], vanadium pentoxide [733,134], sodium vanadate [735], selenium dioxide [725], chromium trioxide [134], ammonium molybdate [736], tungsten trioxide [737], tungstic acid [737],... 

Van Zyl JM, BJ van der Walt (1994) Apparent hydroxyl radical generation without transition metal catalysts and tyrosine nitration during oxidation of the anti-tubercular drug, isonicotinic acid hydrazide. Biochem Pharmacol 48 2033-2042. 

The anti-Markovnikov product was formed with >95% regioselectivity at 35°C. The examples in Scheme 5-21, Eq. (1) show that cyano and hydroxyl functional groups are tolerated by the catalyst, and diphenylphosphine oxide can be added to both C=C bonds in a di-alkyne. The reaction also worked for internal alkynes (Scheme 5-21, Eq. 2). Unusual Markovnikov selectivity was observed, however, for 1-ethynyl-cyclohexene (Scheme 5-21, Eq. 3) [17]. 

The zirconocene catalysts described above are very oxophilic, which provides several synthetically useful transformations. Oxygen substitution at the al-lylic or homoallylic position of an olefin substrate allows for excellent regio-and diastereocontrol in the ethyl magnesiation reactions of a-olefins and dienes [21]. When 29 is substituted with a hydroxyl group (29a), syn 30a is favored over anti in a 95 5 ratio, while substitution with OCH3 (29b) reversed the diastereoselectivity to 11 89 (Eq. 6). Use of THF in place of diethyl ether as the reaction solvent for the reaction of 29a lowered the overall diastereo-... 

The hydrogenation of acyclic homoallylic alcohols with a 1,1-disubstituted ole-fmic bond by cationic [Rh(diphos-4)]+ catalyst proceeds in modest to moderate stereoselectivity, generally forming 1,3-anti compounds (Table 21.10, entries 1, 4 and 5), and the effect of the stereogenic center at the allylic position overrides the directivity of hydroxyl group. The 1,3-syn product is then observed though in poor selectivity (entry 3) [19, 57, 58]. Inspection of the hydrogenation prod-... 

Hydroxyl groups reacted with acetic anhydride and pyridine catalyst to form esters. Capillaries empty. Anti-shrink Efficiency (ASE) about 70%. 

Recently, Sames and co-workers showed an interesting application, in which it was demonstrated that the Shilov chemistry permits heteroatom-directed functionalization of polyfunctional molecules [16]. The amino acid valine (10) was allowed to react in an aqueous solution of the oxidation catalyst PtCU and Cu(ii) chloride as stoichiometric oxidant (Scheme 3). At temperatures >130 °C a catalytic reaction was observed, and a regioselective C-H functionalization delivered the hydroxyvaline lactone 11 as a 3 1 mixture of anti/syn isomers. It was noted that the hydroxylation of amino acid substrates occurred with a regioselectivity different from those for simple aliphatic amines and carboxylic acids. The authors therefore proposed that the amino acid functionalization proceeded through a chelate-directed C-H activation. 

The direct enantioselective a-hydroxylation of activated ketones [22], specifically cyclic / -dicarbonyl compounds, can be performed using dihydroquinine as the chiral catalyst and simple commercially available peroxides as the oxidant. The use of cumyl hydroperoxides led to the a-hydroxylation of / -ketoesters 21 in high yields and moderate to good enantioselectivities (66-80% ee) (Eq. 5). These optically active alcohols (22) undergo a diastereoselective reaction to anti-diols with excellent diastereoselectivity (99 1) using BH3-4-ethylmorpholine as the reducing agent. 

Hayashi et al. used (R)- or (S)-proline as catalysts to hydroxylate the cyclohexanone 127 selectively to get either the intermediate 128 (upon hydrogenolysis of the N—O bond of the primary reaction product), which was converted further to the natural anti-angiogenesis agent RK-805 (129) and similar natural products such as fumagillol and ovalicin (112), or the intermediate 130. The latter could be transformed into (-i-)-panepophenanthrin (131) (113) (Scheme 30), a potent... 

In the same context, Loh et al. have developed the first organocatalytic and enantioselective direct vinylogous Michael addition of a,a-dicyanoolefins to maleimides performed in the presence of the cinchona alkaloid depicted in Scheme 1.26. This novel procedure generated the corresponding Michael anti-products in good yields with excellent diastereo- and enantioselectivities of up to 99% ee, as shown in Scheme 1.26. In this study, the authors have demonstrated that the free hydroxyl group of the catalyst played a key role in the substrate activation. 

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