Alcohols regioselective oxidation

Oxidations catalyzed by NAD(P) -dependent dehydrogenases formation of chiral lactones from /nej o-diols stereoselective formation of ketones from polyfunctional alcohols regioselective oxidations of steroids. 

Based on these results, a novel method for the synthesis of hexose-6-aldehydes from natural carbohydrate sources has been developed by us. Preliminary results for the regioselective oxidation of the primaty alcohol group in glycosides by the dinuclear copper(ll) complex N, A-bis[(2-pyridylmethyl)-l,3-diaminopropan-2-olato] (p-acetato) dicopper(ll) perchlorate (Cu2(bpdpo), (4) are described below. 

A recent report on the regioselective oxidation of lactic acid also seemed consistent with this idea. Photocatalytic oxidation on platinized TiO2 led to decarboxylation, while that on platinized CdS led to pyruvic acid by oxidation of the alcohol group, Eq. (6) However, when potentiostatic oxidation of lactic acid was conducted in... 

Such regioselectivities are unique and suggest that redox pillared clays may have broad scope and utility as selective, heterogeneous catalysts for liquid phase oxidations. Indeed, V-PILC also catalyzes the oxidation of benzyl alcohol (to a mixture of benzoic acid and benzylbenzoate) whilst a-methyl benzylalcohol is left completely untouched.71 Similarly, p-substituted benzyl alcohols are oxidized whilst o-substituted benzyl alcohols are inert.71... 

QCC)385 is able to regioselectively oxidize primary alcohols in the presence of secondary ones. Tetrabutylammonium (TBACC),386 387 butyltriphenyl-phosphonium (BTPPCC) and benzyltriphenylphosphonium chloro-chromates, as they possess no acidic protons, behave as very mild oxidants able to perform selective oxidations on allylic and benzylic alcohols. 

There is an initial regioselective oxidation of the primary alcohol into an aldehyde. 

The aldehyde equilibrates with a lactol that is oxidized to a lactone. Thus, the initial regioselective oxidation of the primary alcohol allows a very selective formation of a lactone in the presence of two unreacting secondary alcohols. 

Because of the subtle energetic factors, allowing the oxidation of a certain alcohol employing the Oppenauer conditions, it is possible to carry out regioselective oxidations based solely on thermodynamics.21... 

In 1960, Burn et al.93 found that 2,3-dichloro-5,6-dicyano-p-quinonc (DDQ) (83) was able to perform the regioselective oxidation of allylic sterols in the presence of saturated alcohols in dioxane or benzene at room temperature. 

An allylic alcohol is regioselectively oxidized in the presence of a saturated alcohol with DDQ at room temperature. 

In this tetrol, a single secondary alcohol is oxidized with 88% yield thanks to the formation of the most stable cyclic stannylene intermediate by the regioselective reaction of BU2S11O with one of the 1,2-diol moieties in the molecule. 

A very good yield of hydroxyketone results from the regioselective oxidation of a secondary alcohol using hydrogen peroxide in the presence of catalytic peroxotungstophosphate. 

Chloral or benzaldehyde in the presence of dehydrated alumina48 and Al(OtBu)3 in the presence of f-BuOOH,49 are oxidizing systems reminiscent of Oppenauer oxidations that can perform regioselective oxidations of secondary alcohols. 

Trityl trifluoroborate produces the tritylation of both alcohols and the regioselective oxidation of the resulting secondary trityl ether. The primary trityl ether is hydrolyzed on contact with silica gel during the work-up, resulting in the formation of an 80% yield of the... 

The epoxidation of allylic alcohols can be carried out with peroxy acids in aqueous medium. In the case of polyolefinic alcohols, regioselectivity results from control of the pH of the reaction the proton of the allylic hydroxy group plays a fundamental role when the oxidation is carried out at a high pH296. 

We found that under the conditions of the Wacker oxidation,27 the terminal double bonds of the metathesis products were cleanly transformed to the corresponding aldehydes. While the regioselective oxidation of protected allylic alcohols has been reported,28 the selective Wacker oxidation of an allylic amine derivative to the aldehyde is unprecedented. The Ns protected precursor 19 produced only the starting amine (NsN(H)CH2CH2CH2CH(OEt)2). Consequently, the Ns protecting groups were exchanged with Cbz (27) which successfully led to the desired aldehyde 28. 

The anodic oxidation of secondary alcohols to the corresponding ketones is generally inferior to the catalytic dehydrogenation methods. Electrochemical syntheses are therefore of interest only in special cases. An example of this is the regioselective oxidation of an endo-hydroxyl group in 1,4,3,6-dianhydrohexitols 306) ... 

The regioselectivity of the C-H insertion is mainly controlled by the reactivity of the C-H bonds. For example, in the DMD oxidation of trans-dimethylcyclohex-ane [24] the tertiary C-H bond is selectively oxidized rather than the secondary bonds (Scheme 1). Similarly, when methylcyclohexane (1) is oxidized by TFD, the alcohol 2 (oxidation at the tertiary C-H bond) prevails, as shown in Scheme 2. When the reactivity is similar, the regioselectivity is governed by steric factors. This is well illustrated in Scheme 3 for the steroid pregnane (4), which, for steric reasons, is selectively hydroxylated at the C14 position in the presence of other tertiary C-H bonds (C5, C8, C9 C17, C20) [25]. Similarly, in the TFD oxidation of brassi-nolide (6), only the tertiary C-H bond of the side-chain (position 25) is hydroxylated (Scheme 3) [26],... 

The oxidation of a,p-unsatuiated caibraiyl compounds under the usual conditions in DMF using PdCl2/CuCl/02 is very slow. However, regioselective oxidation of oc, -unsaturated esters to p-keto esters (equation IS), and a,p-unsaturated ketones to 1,3-diketones (equation 16) proceeds with NazPdCU in solvents such as 50% acetic acid, isopropyl alcohol, and NMP. r-Butyl hydroperoxide and hydrogen peroxide are used as the reoxidants of the reduced palladium. The reaction proceeds slowly at room temperature but smoothly between 50 and 80 C. Some typical examples of this process are shown in Table 1. 

In the oxidation of 2-octenyl acetate, in addition to the normal oxidation, palladium-catalyzed allylic rearrangement and subsequent oxidation took place to give a small amount of 3-acetoxy-2-octanone as a byproduct. Ethers of secondary allylic alcohols also underwent the regioselective oxidation to give the corresponding 3-alkoxy ketones in 30-40% yields. But in this case too, by-products derived from the allylic reanangement a subsequent oxidation were also detected. Results of the oxidation of some allyl ethers are shown in Table 3. °... 

The intermolecular coupling of allenes 123 and enones 124 selectively afforded dienones 125 in 53-81% yields (Scheme 4.45) [93]. As a catalyst precursor, [CpRuCl(cod)] was employed with CeCl3 7H20 and an alkynol 126 as activators. The proposed reaction mechanism involves the regioselective oxidative cyclization of the two components on a cationic ruthenium center, leading to the ruthenacyclopentane intermediate 127. When allenyl alcohols 128 were employed under otherwise identical conditions, the final products were cyclic ethers 129 (Scheme 4.46) [94]. As a catalyst precursor, the cationic ruthenium complex 68 can be used in the absence of the alkynol 126. The ether ring was considered to be formed directly via the ruthenacyclopentane 130 or alternatively through its Jt-allyl form 131. 

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