Benzylic alcohols manganese dioxide

Oxidation of allylic or benzylic alcohols. Manganese dioxide prepared by ozoniza-tion of manganese (II) nitrate is an effective agent for oxidation of allylic and benzylic alcohols.38... 

Manganese dioxide (Mn02) supported on silica provides an expeditious and high-yield route to carbonyl compounds. Benzyl alcohols are selectively oxidized to carbonyl compounds by use of 35 % Mn02 doped silica under MW irradiation conditions (Scheme 6.28) [96]. 

An alternative access to murrayanine (9) was developed starting from the mukonine precursor 609. The reduction of the ester group of 609 using diisobutylaluminum hydride (DIBAL) afforded the benzylic alcohol 611. In a one-pot reaction, using very active manganese dioxide, 611 was transformed to murrayanine (9) (574) (Scheme 5.36). 

Alkyl groups can be oxidized, as for example the benzyl group in compound (148), to a benzoyl group by permanganate or (better) by selenium dioxide.42 Similarly, the benzyl alcohol in compound 149 is oxidized by manganese dioxide.87 The thiol 150, treated with ferricyanide, gives the disulfide 151.65 Oxidation of thiol 150 with nitric acid is thought to... 

Manganese dioxide very soon became a widely used standard oxidant for the transformation of allylic and benzylic alcohols into aldehydes and ketones.4 It offers very mild conditions and is extremely selective for allylic and benzylic alcohols when it is not employed at a high temperature. On the other hand, the work-up of oxidations with M11O2 is very simple, involving just filtration of suspended solid and elimination of solvent. 

The selective oxidation of benzylic and allylic alcohols with active manganese dioxide in the presence of saturated alcohols is normally carried out by stirring or shaking a solution of the alcohol in an organic solvent in the presence of 5-20 equivalents of suspended active M11O2. 

Oxidation of sensitive divinyl alcohol 20 to dienone 4 is achieved by treatment with activated manganese dioxide. Commercially available active Mn02 21 is a synthetic nonstoichiometric hydrated material. This reagent provides mild conditions for oxidation of allylic, propargylic, and benzylic alcohols.10... 

Conjugated—a,/)-unsaturated or aromatic—aldehydes are oxidized by manganese dioxide in the presence of one equivalent of sodium cyanide to give an acyl cyanide (Formula C in Figure 17.18) via an intermediate cyanohydrin (B in Figure 17.18), which is also either an allylic or a benzylic alcohol. Alcohols of this kind can be oxidized by a relatively weak oxi-... 

To oxidize the benzylic alcohol function of compound 20, a mixture of this compound and a large excess of manganese dioxide is stirred in dichloro-methane at room temperature under argon for 1.5 h. After a short work-up, compound 21 may be obtained quantitatively (Scheme 9.16). 

Manganese dioxide is extensively used as an oxidizing agent for the oxidation of allylic alcohols to the corresponding aldehydes. Benzylic and unactivated alcohols are also oxidized by Mn02-... 

MnC>2 (manganese dioxide) Hexane benzene dichloromethane 0, RT. Reflux selective for allylic or benzylic alcohols—) aldehydes or ketones... 

A useful addition to the roster of oxidants converting primary alcohols into aldehydes is manganese dioxide, which can be prepared by several methods [805, 806, 807, 808, 809, 810]. It is used as a suspension in petroleum ether [8< 5, 808], ether [806, 808, 811], hexane [806, 811], benzene [808, 813], chloroform [808, 811, 813], and carbon tetrachloride [808, 813]. The oxidations are carried out at room temperature and are especially suitable for allylic and benzylic alcohols, which are oxidized more readily than the saturated alcohols [808, 810], Yields vary widely depending on the substrate, on the ratio of the substrate to oxidant (which in turn depends on the particle size of the oxide [810]), on the solvent, and on the reaction time 811] (equation 214). 

Oxidation of oxygen functions. DDQ is useful for the selective oxidation of allylic " and benzylic alcohols. The reagent has the advantage of not showing the variability encountered with active manganese dioxide. It dehydrogenates 2-hydroxymethylene-3 ketosteroids in about 50% yield. The steroid is treated in dioxane solution at room temperature with 1.1 -1.5 equivalents of DDQ for 1 -5 min.. 

Activated manganese dioxide (MnO2) reliably oxidizes acetylenic, allylic, and benzylic alcohols to aldehydes and ketones. Saturated primary and secondary alcohols are also oxidized, albeit more slowly. The two main concerns are the activity of the manganese dioxide and the slow filtration of salts after the reaction. Activated MnOi is available commercially or may be prepared. 

Preparation [1, 637-638, after citation of ref. 7]. Belew and Tek-Ling7a have prepared an active form of manganese dioxide by ozonization of an aqueous solution of manganese (11) nitrate containing perchloric acid. This material oxidizes benzyl alcohol to bcnzaldehyde in 82% yield. 

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