Chemoselective Oxidation of Alcohols

Scheme 20 Chemoselective oxidation of alcohols with (o-TolbBiC -DBU and Dess-Martin periodinane [82]...

Mannam S, Alamsetti SK, Sekar G (2007) Aerobic, chemoselective oxidation of alcohols to carbonyl compounds catalyzed by a DABCO-copper complex under mild conditions. Adv Synth Catal 349(14-15) 2253-2258... 

Figure 4.10 Chemoselective oxidation of alcohols with Cr-APO-5 in the presence of TBHP.

A chemoselective oxidation of alcohols using potassium periodate (KIO ) in the presence of a catalytic amount of tetramethylammonium bromide (Et NBr) as ionic liquid under microwave irradiation (MW) was reported by Hajipour et al. (Scheme 14.23) [22]. 

Scheme 14.51 Chemoselective oxidation of alcohols using KMnO in [bmim][BF ]...

Oxidations. By using Phl=0 (in presence of KBr) as an oxidant, alcohols are oxidized to acids and ketones in water in excellent yields. When catalyzed by either poly(4-vinylpyridine)-supported sodium ruthenate or a (salen)chromium complex chemoselective oxidation of alcohols (e.g., allylic alcohols to alkenoic acids) occurs, which is contrary to the effect of (salen)manganese and (porphyrin)iron complexes (giving epoxy alcohols). ... 

Miscellaneous Applications. The chemoselective oxidation of alcohols and diols using T 0-i- r)Jt-Butyl Hydroperoxide has been reported. The title reagent has also been employed as a catalyst in Diels-Alder reactions and as an additive in the palladium-catalyzed reaction of aryl-substituted allylic alcohols with zinc enolates of p-dicarbonyl compounds (eq 24). The latter... 

Tanaka A, Hashimoto K, Kominami H (2012) Preparation of Au/Ce02 exhibiting strong surface plasmon resonance effective for selective or chemoselective oxidation of alcohols to aldehydes or ketones in aqueous suspensions under irradiation by green light. J Am Chem Soc 134(35) 14526-14533... 

A double mediatory system consisting of modified TEMPO and halide ion or metal ion was also exploited for the oxidation of alcohols [53-55]. A number of carbohydrates have been chemoselectively oxidized at the primary hydroxyl group to uronic acids [56]. 

More recently, the Noyori group described an organic solvent- and haUde-free oxidation of alcohols with aqueous H202 . The catalyst system typically consists of Na2W04 and methyltrioctylammonium hydrogen sulfate, with a substrate-to-catalyst ratio of 50-500. Secondary alcohols are converted to ketones, whereas primary alcohols, in particular substituted benzyUc ones, are oxidized to aldehydes or carboxylic acid by selecting appropriate reaction conditions This system also catalyzed the chemoselective oxidation of unsaturated alcohols, the transformation exemplified in equation 65, with a marked prevalence for the hydroxy function. 

Step 1. Chemoselective oxidation of the primary alcohol (diacetoxyiodo)benzene (DIB) is the stoichiometric co-oxidant. 

Table 26 Summary of the results obtained for the chemoselective oxidation of primary alcohols...

Chemoselective oxidation of the allylic alcohol in triol 865 with manganese dioxide followed by in situ cyclization and oxidation of the resulting 5,6-dihydropyran-2-ol provides the 5,6-dihydropyran-2-one subunit 866 of bryostatin (Equation 349) <20000L2189>. 

The chemoselective oxidation of a primary alcohol in the presence of a secondary alcohol is a somewhat more difficult task. Not only is the inherent difference in reactivity less than in the case of the selective oxidation of allylic alcohols discussed above, but most reagents will oxidize secondary alcohols somewhat more rapidly than primary alcohols. Nevertheless there are reagents which will carry out the selective oxidation of a primary alcohol to an aldehyde without oxidizing a secondary alcohol, some of which will be considered here. 

This type of chemoselectivity has been observed in the oxidations of alcohols using copper(II) chloride and a catalytic quantity of 2,2,6,6-tetramethylpiperidinyl-l-oxyl (11 equation 11). The oxidizing species which is generated, in fw example the oxidation of (12) to (13), is the cation (14), which may also be produced using electrochemicai oxidation (in the wesence of the weak base 2,6-lutidine). Allylic and ben lic alccAols are easily oxidized by this reagent, whereas secondary alcdiols react slowly. 

Examples of the highly chemoselective oxidation of a secondary hydroxy group have been reported using bromine in the presence of bis(tri-n-butyltin) oxide (equations 36 and 37), primary alcohols being essentially inert to this reagent mixture. ... 

Benzyltrimethylammonium tetrabromooxomolybdate will catalyze the chemoselective oxidation of secondary alcohols with r-butyl hydroperoxide as cooxidant.Remote double bonds can interfere with this oxidation, and 1,2-diols are converted into 1,2-diketones (Scheme 19). 

There are numerous reagents available for the chemoselective oxidation of polyfunctional alcohols. The most promising general type of oxidant must be that in which a mild, clean oxidizing agent e.g. t-buQ l hydroperoxide, bromine, air orN-methylmorpholineN-oxide) is used in conjunction with a reagent which will catalyze the desired selective oxidation. Mild, stoichiometric oxidants (such as periodinane). 

The chemoselective oxidation of a saturated secondary alcohol in the presence of a saturated primary alcohol is possible with a number of reagents. N-Bromosuccinimide in an aqueous organic solvent has been used to carry out this type of selective oxidation and has found use in synthesis. The value of this reagent is exemplified by its use in the synthesis of isocyanopupukeanane and in work towards a total synthesis of gelsemine (equations (32) and (33) respectively). Clearly this reagent would not be compatible with all functional groups, given the well-known reactivity of N-bromosuccinimide towards unsaturated compounds. 

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