Molybdenum secondary alcohols

Certain molybdenum complexes, such as MoO(02)(PhCONPhO)22 and the peroxo-molybdenum compound derived from tris(cetylpyridinium) 12-molybdophosphate and hydrogen peroxide (PCMP),28 are able to selectively oxidize secondary alcohols. PCMP is able to perform selective oxidations in catalytic amounts in the presence of hydrogen peroxide as secondary oxidant.29... 

Other molybdenum complexes able to catalyze the selective oxidation of secondary alcohols are ammonium molybdate in the presence of H202,30 benzyltrimethylammonium tetrabromooxomolybdate in the presence of r-BuOOH31 and molybdenum hexacarbonyl in the presence of catalytic cetylpyridinium chloride and stoichiometric t-BuOOH.32... 

Several compounds of tungsten, which is a transition metal closely related to molybdenum, are able to catalyze the selective oxidation of secondary alcohols with hydrogen peroxide as secondary oxidant. These include tris(cetylpyridinium) 12-tungstophosphate,33 peroxotungstopho-sphate (PCWP)34 and Na2W04 in the presence of a phase transfer catalyst.35 Tungstophosphoric acid is able to catalyze the selective oxidation of secondary alcohols in the presence of ferric nitrate as secondary oxidant.36... 

Several procedures for this chemoselective oxidation utilize molybdenum-based catalysts, with either hydrogen peroxide or r-butyl hydroperoxide as the stoichiometric oxidant. These include ammonium molybdate in the presence of a ph e transfer reagent and hydrogen peroxide, which with pH control (potassium carbonate) will selectively oxidize a secondary alcohol in the presence of a primary alcohol without oxidizing alkenes. In addition hindered alcohols are oxidized in preference to less hindered ones (Scheme 18). 

Ruthenium tetroxide, generated in situ from a suspension of the dioxide in CCI4, by adding aqueous sodium metaperiodate, appears to be an excellent reagent for the oxidation of secondary alcohols in neutral or basic media. t-Amyl or cumyl hydroperoxide, with molybdenum pentachloride, readily oxidizes steroidal alcohols cholesterol affords the 5a-hydroxy-3,6-dione in good yield. ... 

The traditional method of using Cr(IV)-based oxidants is obviously unacceptable today. A number of new environmentally benign catalyst systems have recently been developed which can be used with H2O2 or TBHP as oxidant. These promote chemoselective oxidation of secondary alcohols and diols to ketones, an important class of reactions in organic synthesis. The metals used are molybdenum (Kurusu and Masuyama, 1986) and titanium. 

Oxidation of Alcohols. Diphenyl sulfoxide has been employed as an oxidant in conjunction with molybdenum (VI) and osmium (VIII) catalysts for the conversion of alcohols to carbonyl compounds. Diphenyl sulfoxide in combination with catalytic quantities of Mo02(acac)2 oxidizes alcohols to ketones or aldehydes. Higher yields are obtained with allylic or benzylic alcohols. Catal)dic OSO4 in association with Ph2SO can oxidize primary and secondary alcohols to aldehydes and ketones in the... 

Gas-phase catalytic cycles for the two-electron oxidation of primary and secondary alcohols to aldehydes and ketones by molybdenum complexes its process was found to be analogous with industrial oxidation of methanol to formaldehyde using M0O3. 

Oxidative Methods.—Oxidation of Alcohols. Benzoyl peroxide catalysed by nickel(ii) bromide gives high yields of aldehydes and ketones from the corresponding alcohols. Similar yields are obtained with t-butyl hydroperoxide catalysed by diaryl diselenides, a method particularly recommended for benzylic or allylic alcohols. Ketones are obtained from secondary alcohols using hydrogen peroxide catalysed by molybdenum or tungsten peroxo-complexes/ and nickel peroxide has been employed to prepare a-allenic aldehydes and ketones from allenic alcohols. ... 

Oxidative Methods.— The oxidation of alcohols to carbonyl compounds using DMSO activated by electrophiles, e.g. oxalyl chloride or trifluoroacetic anhydride, has been reviewed/ DMSO-Metal oxide oxidations of alcohols have been described using molar, or catalytic, amounts of a new oxide of molybdenum/ This yellow oxide, Mo-y , is prepared by hydrogen peroxide oxidation of molybdenum or its trioxide/ N Iodosuccinimide in combination with tetra-butylammonium iodide oxidizes primary and secondary alcohols to aldehydes and ketones in dichloromethane solution/ The corresponding bromo-combina-tion gave inferior yields, and the chloro-combination resulted in polychlorination of the carbonyl product. 

The molybdenum peroxo-complex (3) oxidizes primary and secondary alcohols, but epoxidizes allylic alcohols. Chlorosulphonyl isocyanate is a further electrophile which may be used to activate DMSO in the oxidation of alcohols. In the presence of triethylamine, a wide variety of alcohols may be oxidized at -78 °C, in high isolated yield. 

Alkyl hydroperoxides oxidize some sugar alcohols to the corresponding ketones under molybdenum-salt catalysis. Ruthenium tetroxide oxidizes secondary alcohols to ketones in neutral or basic media permitting, under the latter conditions, direct conversion of y-lactones into y-ketoacids. ... 

The synthesis, structures and function of caibohydiate-metal coordination conqmunds has beoi reviewed. Conqilexes of some hepurfiiranose derivatives containing primary-secondary 1,3-diol moieties with molybdenum tetraacetate have been studied and their CD spectra have allowed assignment of die configurations (rf the secondary alcohol centres. Aldoses of the arabino- and xylo- series have been shown to form tetradentate acyclic complexes with molybdare ions in aqueous acidic media, and the structure and conformation of molybdare conqil ces with S-deoxy-L-arabinose and S-deoxy-L-ribose have been studied. Molybdate complexes of D-allose, D-altrose, D-gulose and D-idose have been studied by NMR methods. ... 

In acyclic secondary -allylic alcohols, epoxidation by the vanadium system shows opposite stereospecificity to that of peracid and molybdenum carbonyl-mediated epoxidation (see Scheme 6)22 The predominance of the erythro isomer in the former process is rationalized22 in terms of the energetically more favorable transition state (6, cf. 5) and in this context the mechanism has analogy in the epoxidation behavior of medium-ring cyclic allylic alcohols.23... 

Muzart s group has recently described the use of molybdenum catalysts with the hydrogen peroxide adduct, sodium percarbonate and a phase-transfer agent.198 The molybdenum catalyst used in the study was Mo02(acac)2, and the solvents screened were dichloroethane and acetonitrile. The active species is a Mo peroxo complex and in common with other methods based on Mo and W catalysts, secondary, allylic and benzylic alcohols react quickly, and give higher yields of carbonyl product than primary aliphatic alcohols. 

Molybdenum and vanadium compovmds have also been widely investigated as catalysts for the oxidation of alcohols with tert-butyl hydroperoxide (TBHP) as the oxidant. With the former a peroxometal pathway is involved while with the latter an oxovanadium(V) intermediate is the active oxidant. As with the H202-based systems described above, these systems exhibit a preference for the oxidation of secondary hydroxyl functionalities over primary ones. In contrast, zirconyl acetate, SO(OAc)2, catalyzes the selective oxidation of primary alcohol moieties with TBHP (Reaction 29) °". ... 

Two separate reports on the vanadium-catalysed epoxidation of allylic alcohols have appeared. In the case of secondary acyclic E -allylic alcohols opposite stereospecificity to peracid and molybdenum-catalysed systems is observed. This... 

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