Regiospecific oxidation

Oxidation Products of Sucrose. The essentially regiospecific oxidation by Agrobacterium tumefaciens, whose dehydrogenase exclusively generates 3 -ketosucrose, is the prototype of an entry reaction into modified sucroses. This ready access opened the way to manifold modifications at the 3 -carbonyl function (Scheme 2.16)." Chemical oxidation proceeds less uniformly, for... 

Heme oxygenase catalyzes the regiospecific oxidation of heme to bili-verdin (Fig. 6) and has been isolated and purified from several sources 247-251). In mammals, the enzyme is membrane-boimd, a complication... 

Optically active A-ethyl and A-benzylpiperidine gave the 2,6-diones with RuO / aq. Na(IO )/CCl (Table 5.1) [404,405]. Regiospecific oxidations of 2-substimted -... 

In related work, carbohydrate 1,2-diol dibutylstannylene acetals have been regiospecifically oxidized by IV-bromosuccinimide to give a-hydroxy-ketones. The reaction is illustrated for the preparation of 3-deoxy-l,2-O-isopropylidene-a-D-eryt/zro-hexofuranos-5-ulose (223) in Scheme 24. The endocyclic diol is also regioselectively oxidized to one product (224) in 44% yield, although 55% of the starting compound was recovered. (Scheme 24).439a... 

Benzoquinones such as (227) have been prepared by regiospecific oxidative prenylation of the corresponding methylhydroquinone with Me2C=CHCH2Br in the presence of /3-cyclodextrin. Detailed descriptions are available of methods for the preparation of ubiquinone analogues,and the synthesis of some new ubiquinone analogues, e.g. (228), has been reported. ... 

The regiospecific oxidative nitration of 3,4-dihydro-6,7-disubstituted quinoxalin-2(l//)-ones utilizing fuming nitric acid in trifluoroacetic acid gives 5-nitro-6,7-disubstituted quinoxa-line-2,3(l/f,4/f)-diones in good yields. 

The regiospecific oxidation of dimethylanisoles to methoxymethyl-benzaldehydes is accomplished with copper sulfate and potassium peroxy-disulfate, which oxidize selectively only the methyls in the ortho or para positions with respect to the methoxy group (equation 171) [35J]. 

Regiospecific oxidation of the 3-hydroxy-group of methyl fusidate has been accomplished by use of the Corey reagent (one equivalent of AT-chlorosuccinimide-dimethyl sulphide complex). 

Regiospecific oxidation of the C-4 sodium enolate of furanone (132) gave the C-4 hydroxy furanone (133) as a single diastereomer in 80% yield <94TL1477>. The same sequence was used to prepare the C-2 alcohol (134) after TMS protection of the C-4 hydroxy group (Scheme 26). 

It has been established that thiophenes undergo regiospecific oxidative cyanation at C-2 with TMSCN, as illustrated by the general transformation of 41 into 42 <05OL537>. Conversion of 3-bromobenzo[6]thiophene to benzo[6]thiophene-3-carbonitrile has been accomplished by treatment of the substrate with Zn(CN)2 in the presence of a catalytic system consisting of Pd/C, Zn dust, Br2, and PPhs in A/jA -dimetliylacetamide <05TL 1849>. 

DAVID-MUKAIYAMA-UENO Selective Diol Oxidation Regiospecific oxidation of diols to ketoalcohols by Br2 via Sn derivatives. 

The same allylic alcohols (142) undergo regiospecific oxidative cleavage with pyridinium chloro-chromate at the ethylenic bond to give, after saponification, a-hydroxyacids (145). Extension of this reaction to a -unsaturated ketones (146), obtained by oxidation of secondary alcohols with silver carbonate on celite, affords a-ketoacids (147) <88TL626l>. 

But the regiospecific oxidation of olefinic compounds by palladium catalysts is enjoying increasing importance as a step in the multistep syntheses of complex organic compounds such as pharmaceuticals, pesticides, and fragrances. The carbonyl compounds are reactive intermediates in such syntheses. 

The chemoenzymatic synthesis of (13S)-hydroxy-18 2(9Z,ll ) was achieved in nine steps starting from (2 )-octenal. Of importance was the enzymatic conversion of (2 )-octenal to the (5)-cyanohydrin [5] with (S)-hydroxynitrile lyase cloned from Hevea brasiliensis (41). 13- Hydroxy-lO-oxo-18 1(11 ) was synthesized via a Kno-evenagel-type reaction of Isopropyl 11 - phenylsulfinyl-10-oxoundecanoate with hep-tanal to form y-hydroxyenone functionality together with carbon chain elongation (42). The regiospecific oxidation of a number of substituted unsaturated fatty esters with /7-benzoquinone in the presence of palladium(II) chloride under concomitant ultrasonic irradiation was reported. For example, methyl 9-hydroxy-18 1 (12Z) furnished methyl 9-hydroxy-12-keto-18 0 exclusively (43). 

Lie Ken Jie, M.S.F., andC.K. Lam, Regiospecific Oxidation ofUnsaturated Fatty Esters with Palladium(II) Chloride/p-Benzoquinone A Sonochemical Approach, Chem. Phys. Lipids 81 55-61 (1996). 

Grustacean chitins were submitted to regiospecific oxidation at G-6 with NaOGl in the presence of the stable nitroxyl radical 2,2,6,6-tetramethyl-l-... 

Carboxylic acids from 2,3-dihydro-1,4-dioxins via regiospecific oxidative ring opening... 

DichlorO 5,6-dicyanoquinonelacetic acid Aryloxo compds. from alkylarenes Regiospecific oxidation... 

Synthesis of AU Iidene 1,2-Oxasiletanes. The regiospecific oxidation of siliranes to 1,2-oxasiletanes can be accomplished in moderate yield with diphenyl sulfoxide. When 1,1-dimesityl-2Z-neopentylidenesilirane was heated with diphenyl sulfoxide in benzene, 2,2-dimesityl-4Z-neopentylidene-l,2-oxasiletane was formed in 70% yield (eq 11). In contrast, use of cyclo-hexyldimethylamine A-oxide instead of diphenyl sulfoxide gave the isomeric 1,2-oxasiletane in 44% yield along with mesitol in 40% yield (eq 12). 

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