Hydroxylation of adamantane

The ruthenium-substituted sandwich-type POM WZnRu2(OH)(H20)(A W9034)2]11 (X- Zn2+ or Co2+, Figure 13.1) catalyzed the selective hydroxylation of adamantane with Oz as an oxidant[58,59] ... 

Ru(CO)(TPFPP) (TPFPP=5,10,15,20-tetrapentafluorophenylporphyrinate) is made from the hgand and RUjCCO),. The system Ru(CO)(TPFPP)/(Cl2PyNO)/ CH2Cy65°C catalysed the hydroxylation of adamantane and of c/x-and trans-decalm, with high selectivity and complete stereoretention, and epoxidised 1-octene. Intermediacy of a TPFPP-Ru(lll) and an oxo-Ru(V) species was proposed [877]. 

RuCl(dmso)(tpa)](PF ) and RuCl(dmso)(BPG) (tpa=tris(2-pyridylmethyl) amine, BPG=A,iV-bis(2-pyridylmethyl)glycmate) no preparation was given. The X-ray crystal structure of the (tpa) complex showed sulfur co-ordination from (dmso). As [RuCl(dmso)(tpa)](PFg) and RuCl(dmso)(BPG)/MCPBA/CHCl3 they catalysed hydroxylation of adamantane [951]. 

Selective poly hydroxylation of adamantane is possible.87 A concerted insertion mechanism closely resembling to the mechanism of ozonation has been... 

Figure 4. (A) Competitive hydroxylation of adamantane/adamantane-

This dry ozonation procedure is a general method for hydrox-ylation of tertiary carbon atoms in saturated compounds (Table 1). The substitution reaction occurs with predominant retention of configuration. Thus cis-decalin gives the cis-l-decalol, whereas cis- and frans-l,4-dimethylcyclohexane afford cis- and trans-1,4-dimethylcyclohexanol, respectively. The amount of epimeric alcohol formed in these ozonation reactions is usually less than 1%. The tertiary alcohols may be further oxidized to diols by repeating the ozonation however, the yields in these reactions are poorer. For instance, 1-adamantanol is oxidized to 1,3-adamantane-diol in 43% yield. Secondary alcohols are converted to the corresponding ketone. This method has been employed for the hydroxylation of tertiary positions in saturated acetates and bromides. 

The tra x-[Ru (0)2(por)] complexes are active stoichiometric oxidants of alkenes and alkylaro-matics under ambient conditions. Unlike cationic macrocyclic dioxoruthenium I) complexes that give substantial C=C bond cleavage products, the oxidation of alkenes by [Ru (0)2(por)] affords epoxides in good yields.Stereoretentive epoxidation of trans- and cw-stilbenes by [Ru (0)2(L)1 (L = TPP and sterically bulky porphyrins) has been observed, whereas the reaction between [Ru (0)2(OEP)] and cix-stilbene gives a mixture of cis- and trani-stilbene oxides. Adamantane and methylcyclohexane are hydroxylated at the tertiary C—H positions. Using [Ru (0)2(i)4-por)], enantioselective epoxidation of alkenes can be achieved with ee up to 77%. In the oxidation of aromatic hydrocarbons such as ethylbenzenes, 2-ethylnaphthalene, indane, and tetrahydronaphthalene by [Ru (0)2(Z>4-por )], enantioselective hydroxylation of benzylic C—H bonds occurs resulting in enantioenriched alcohols with ee up to 76%. ... 

A further use of the system is to mediate the reaction of adamantane with carbon monoxide and oxygen to form 1-adamantanecarboxylic acid . When long-wavelength light (>300 nm) is used, hydroperoxides efficiently generate hydroxyl radicals without the use of metal ions and would be an extremely useful source of hydroxyl radicals, particularly in the design of DNA-cleaving molecules . ... 

It has been also found that PhIO as an oxidant in the presence of a catalytic amount of sulfonated manganese and iron porphyrin supported on poly(vinylpyridinium) polymers in olefin epoxidation and alkane hydroxylation is a better oxidant than Bu4NHS05 °. Oxidation of adamantane to 1-adamantanol in good yield using BU4NHSO5 and acetone in the presence of aqueous NaHCOs was also reported . ... 

This catalyst is known as a highly active catalytic system for the nonradical hydroxylation reaction of adamantane, in which turnovers per hour of 48,000 are observed and only C3-H is hydroxylated selectively. Its high activity makes the oxidation of the stable C-H bond of benzene possible. However, it was impossible to terminate the oxidation at phenol, and quinone was the final product observed. 

Thus, the substituted heteropolyanion is stable and active even in the presence of oxidants such as /-BuOOH or PhIO. Note that the heteropolyanion is unstable with respect to hydrogen peroxide. Based on the high stability, TMSP can be used for alkane hydroxylation [67b]. Mansuy et al. have reported that P2Wn06i (Mn3+ Br)8 is oxidation resistant and more active for the epoxidation of cyclooctene with PhIO than those containing Fe3+, Co2+, Ni2+, or Cu2+ [68]. The oxygenations of cyclohexane, adamantane, and heptane and the hydroxylation of naphthalene, are also catalyzed by TMSP. 

Bridgehead carbons of adamantane [86], pinane [87], and fused norbornanes [85a, 88] undergo selective hydroxylation under similar reaction conditions. Alkyl-substituted cyclopropane is oxidized selectively at the a-position to cyclopropane ring (Eq. 3.54) [89]. The methyl group of toluene can be converted into the corresponding carboxylic acids (Eq. 3.55) [91]. 

Hydroxylation of alkanes preferentially occurs at the more nucleophilic tertiary C—H positions, but some of these systems using 2-mercaptoethanoF or metallic iron powder d hydroxylate adamantane with preference for the secondary position. However, none of these systems hydroxylates cis-decalin with retention of configuration at the hydroxylated atom. ... 

An interesting use for the anhydrous reagent, at least that prepared by the Union Carbide process, is for generation of hydroxyl radicals. Prior to publication of the method by Heywood, Phillips, and Stansbury, Schleyer and Nicholas reported an experiment in which Dr. Heywood of Union Carbide carried out the oxidation and they worked up the reaction mixture. A mixture of 150 g. of adamantane... 

The kinetics of product evolution in a typical reaction of adamantane hydroxylation showed an initial induction period followed by a fast, apparently zero-order phase with the maximum rate and highest efficiencies (Fig. 2). Deviation from linear behavior took place only after 90% oxygen donor and 80% of the substrate had been consumed. When Ru (TPFPP)(0)2, prepared by reaction of Ru"(TPFPP)(CO) with 3-chloroperbenzoic acid was used as the catalyst, no induction time was detected and zero-order kinetics were observed as well. The well defined and characteristic UV-vls spectra of metalloporphyrins provide an invaluable tool for the mechanistic studies. Thus, monitoring the state of the metalloporphyrin catalysts during the course of both model reactions by UV-vis spectroscopy revealed that the initial form of the catalyst remained the predominant one throughout the oxidation, i.e. in the Ru°(TPFPP)(CO) catalyzed reaction c.a. 80% of the porphyrin catalyst existed as Ru"(TPFPP)(CO) and in Ru (TPFPP)(0)2 catalyzed reaction more than 90% of... 

The competitive oxidation of a 1 1 mixture of adamantane and adamantane-rZ/s catalyzed by Ru TPFPP)(0)2 showed a kinetic isotope effect, kn/ko = 4.8 at 40°C (Fig. 4A). Significantly, the deuterated and undeuterated substrates displayed similar turnover rates (kn/ko = 1.2) for hydroxylation in separate reactions (Fig. 4B). 

Figure 5. Eyring plot of adamantane hydroxylation catalyzed by Ru VtPFPP)(0)2...

Similar results were obtained with Ru (TPFPP)(CO) as the catalyst [5]. A kinetic scheme consistent with this observation is as follows as long as the oxidant OD is present in excess, the active Ru(III) catalyst will exist as the adduct Ru(III)-OD. The reactive oxoRu(V) would then be formed in the rate determining step, which is independent of the concentration of the oxidant (OD) (Fig. 3). The temperature dependence of adamantane hydroxylation yielded a linear Eyring plot for the observed rate constants determined over the range of 25 - 65°C with an apparent = 19 kcal/mol (Fig. 5). 

Potassium hydrogenperoxysulfate has been used alternatively to hypochlorite as primary oxidant in phosphate buffer (pH 6-7)/dichloromethane with the Mn por-phyrin/tetraalkylammonium chloride system at room temperature. Very fast al-kene epoxidations and hydroxylations of hydrocarbons (cyclohexane, adamantane, decalins, etc.) were observed. Methoxybenzenes were also oxidized [78]. 

Hydroxylation of tertiary carbon atoms on silica gel. Israeli chemists have devised an experimental method for hydroxylation of saturated hydrocarbons at tertiary positions by ozone adsorbed on silica gel in this way concentrations of ozone of 4.5% by weight at -78 can be attained. First the hydrocarbon is impregnated on the silica gel and then ozone is passed through at -78° until the silica gel is saturated. After the silica gel has warmed to 20, the product is eluted. Tertiary alcohols can be obtained in this way in high yield with almost complete retention of configuration. The secondary alcohol adamantane-2-ol was oxidized to the ketone by this method. 

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