Oxidation chemoselective

The synthesis, X-ray structure and solid state NMR of 4,4-dimethyl-l,2-ditellurolane 75 have been reported <98PS(136-8)291>. Chemoselective oxidation of 1,2-dithiole derivatives using dimethyldioxirane to give products such as 76 has been described <00SUL169>. Cycloaddition of dihydroquinoline-fused l,2-dithiole-3-thiones 77 with DMAD gives the spiro 1,3-dithioles 78 <99CHE587>. Dicationic thiatelluroles such as 79 have been prepared <00AG(E)1318>, anti cancer properties have been claimed for the simple dithiolopyrrolones... 

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]. 

Fig. 27 Chemoselective oxidation of primary OH-groups in carbohydrates with TEMPO as mediator [143-145],...

Chemoselective oxidation of 3-arylsul-fenylmethyl-A -cephem affords 3-meth-oxymethyl-A -cephem in an anodic substitution. From the two thioethers, the arylthio group is more easily oxididized to a radical cation, that then undergoes cleavage to a thiyl radical and a carbocation (Fig. 31) [152]. 

For the quinone imine cyclization of iron complexes to carbazoles the arylamine is chemoselectively oxidized to a quinone imine before the cyclodehydrogenation [99]. The basic strategy of this approach is demonstrated for the total synthesis of the 3-oxygenated tricyclic carbazole alkaloids 4-deoxycarbazomycin B, hyellazole, carazostatin, and 0-methylcarazostatin (Scheme 17). 

With both building blocks 103 and 109 in hand, the total synthesis of lb was completed as shown in Scheme 17. Coupling of acid 103 and alcohol 109 under Yamaguchi conditions to give ester 110 and subsequent desilylation followed by chemoselective oxidation provided hydroxy acid 111. Lactonization of the 2-thiopyridyl ester derived from 111 in the presence of cupric bromide produced the macrodiolide 112 in 62% yield, which was finally converted to pamamycin-607 (lb) via one-pot azide reduction/double reductive AT-methylation. In summary, 36 steps were necessary to accomplish the synthesis of lb from alcohols 88 and 104, sulfone 91, ketone 93, and iodide rac-97. 

Electrophilic substitution at the arylamine 709 using the complex salt 602, provided the iron complex 725 quantitatively. Sequential, highly chemoselective oxidation of the iron complex 725 with two, differently activated, manganese dioxide reagents provided the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727) via the non-cyclized quinone imine 726. Demetalation of the tricarbonyliron-complexed 4b,8a-dihydrocarbazol-3-one (727), followed by selective O-methylation, provided hyellazole (245) (599,600) (Scheme 5.70). 

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

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. 

Oxidation of cyclic ethers to lactones (1, 988). A systematic study of this reaction has been reported. In general, yields are good to excellent by either stoichiometric or catalytic procedures. No anhydrides from further oxidation are detected. The oxidation is chemoselective. Oxidation of a secondary position takes precedence over oxidation of a tertiary site. Primary positions are attacked in preference to secondary positions in the oxidation of acyclic ethers.1... 

A recent method for the highly chemoselective oxidation of sulfides to sulfones using Af-methylmorpholine IV-oxide (NMP) and a catalytic perruthenatc was found to be also applicable in the presence of isolated or allylic double bonds [115]. 

With oxidative reagents of a nucleophilic nature such as sodium and potassium permanganate, sulfoxides react faster than sulfides and a chemoselective oxidation of a sulfoxide in preference to that of a sulfide is available [77-79]. 

A mild and chemoselective oxidation of trifluoromethanesulfenyl chloride to trifluoromcthane-sulfinyl chloride in high yield is achieved using 3-chloroperoxybenzoic acid (Table 19).308 When dilute nitric acid is applied in the oxidation of dichlorofluoromethanesulfenyl chloride, then the corresponding sulfonyl chloride is obtained in low yield (Table 19),309-310 Sullenamidcs... 

Chemoselective oxidation of 4-methoxyanilines to quinonimines can be achieved in the presence of tricarbonyl(ri4-cyclohexadiene)iron complexes. This transformation has been used for the synthesis of carbazoles via intermediate tricarbonyliron-coordinated 4b,8a-dihydrocarbazol-3-one complexes (Scheme 1.24) [57]. 

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

Mechanisms have been proposed for ruthenium(III)-catalysed oxidation of leucine by acid bromate133 and for the chemoselective oxidation of vicinal diols to a-hydroxy ketones with NaBrC>3/NaHS03 reagent.134... 

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... 

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>. 

E)-3-Arylidenethiochroman-4-oncs possess thioether and oi,[)-unsaturatcd ketone functionalities both of which are susceptible to oxidation by DMD. In fact, chemoselective oxidation at sulfur is observed with a separable mixture of the sulfoxide and sulfone being produced in >5 1 ratio. A similar situation holds for the related thioflavanones. Epoxidation of the alkenic double bond in the thiochromanone 1,1-dioxides alone can be achieved using methyl(trifluoromethyl)-dioxirane (Scheme 65) <1994T13113>. However, reaction of NaOCl with 3-arylidenethioflavanones gives the epoxide and subsequent oxidation with DMD then gives a mixture of the sulfoxide and sulfone <2003MRC193>. 

Fig. 14.35. Chemoselective oxidations of an unsaturated ketone the imido peracid A epoxidizes the C=C double bond, while the peracid B reacts with the C=0 double bond causing a Baeyer-Villiger rearrangement...

Tonami H, Uyama H, Kobayashi S et al (2000) Chemoselective oxidative polymerization of m-ethynylphenol by peroxidase catalyst to a new reactive polyphenol. Biomacromolecules 1 149-151... 

Chemoselective oxidation of sulfenimines 2 is a useful method for the preparation of sulfinimines 3.10-12 The oxidation was usually carried out with m-CPBA (3-chlo-roperbenzoic acid) in a biphasic mixture of chloroform and aqueous sodium bicarbonate and a variety of sulfinimines have been prepared in this way. Sulfinimines 3 were usually obtained as a single -isomer despite the fact that their precursors 2 may exist as mixtures of E- and Z-isomers.10 Other oxidants which have been demonstrated to be effective for oxidation include MMPP (magnesium monoperoxyphthalate)13 and chlorine.14,15... 

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