Regioselective oxidations

Allyllic ether 53 is oxidized regioselectively to the /3-alkoxy ketone 54, which is converted into the a,/i-unsaturated ketone 55 and used for annulation[99]. The ester of homoallylic alcohol 56 is oxidized mainlv to the 7-acetoxy ketone 57[99]. 

Oxidation of cyclic and acyclic hydroxylamines with yellow mercuric oxide appears to proceed with high regioselectivity (109-115). Regioselectivity is determined by the electronic nature of the substituents (116). The oxidative regioselectivity of Mn02 is comparable to that of HgO, but due to its lower toxicity, it has been proposed to use Mn02 rather than HgO (Table 2.2) (117). 

Various mono- or di-olefins were oxidized regioselectively to their epoxides in high yield with the 2-nitrobenzenesulfonylperoxy intermediate 51 generated in situ from 2-nitrobenzenesulfonyl chloride and KO2 at —35°C in CH3CN (equation Thus /3-... 

Hypervalent iodine(lll) was shown to catalyze the direct cyanation of iV-tosylpyrroles and -indoles under mild conditions, without the need for any prefunctionalization <2007JOC109>. Phenyliodine(m) bis(trifluoroacetate)-induced oxidative regioselective coupling of pyrroles in the presence of bromotrimethylsilane gave a series of electron-rich bipyrroles <2007S2913>. 

HydroxylatUm of resorcinol ethers Methyl or THP ethers of resorcinol are oxidized regioselectively by w-chloroperbenzoic acid in CH2CI2 at 0° to derivatives of 1,2,4-trihydroxybenzene in yields of 55-80%. 

Thus, more improvement is still necessary for the oxidation of internal alkenes. However, internal alkenes with some functional groups at suitable positions are oxidized regioselectively by participation of the functional groups under proper conditions as surveyed in the following sectioiL... 

Diketones were obtained mainly by the oxidation of y,8-unsaturated ketones and used for cyclopentenone anellation. 2 > One example is shown below (equation 17). However, the following y,8-unsaturated lactone was oxidized regioselectively to give 1,5-ketolactone in 73% yield in one week (equation 18). ... 

Compounds 120 can also be oxidized regioselectively to afford aminonitrones 122. The X-ray structural analysis of 122 (Ar =/)-MeC6H4) shows an unexpected tautomeric fixation of the hydrogen atom and indicated that the resonance structures 122 and 122" participate in the stabilization of the nitrone 122. Thus, compounds 122 are unusually stable due to the contributions of anionic as well as cationic delocalized mesomeric structures (Scheme 26) <2000JPR245, 1999H(51)763>. 

Limonene is oxidized regioselectively by PBA (Eq. 8) and stereoselectivity can be observed for endo- and exo-dicyclopentadienes. ... 

Oxiranes can be prepared by electrochemical oxidation. " Regioselective w-epoxidation of polyisoprenoids will take place with excellent yields on sodium bromide-promoted electrochemical oxidation in neutral or basic medium. " " This has now been described as a general method. " " Hexafluoropropylene oxiranes have been produced by electrochemical means. " The deoxygenation of dioxetane to oxirane with triphenylphosphine has been described (Eq, 50). ... 

Saegusa oxidation Regioselective introduction of the carbon-carbon doubie bond to cyciic and acyiic ketones yia Pd-mediated oxidation of the corresponding siiyi enol ethers. 390... 

Baeyer-ViUiger oxidation. 3-Trimethylstannylcyclohexanones are oxidized regioselectively. With the added NaHCOj the lactone products are decomposed and 5-hexenoic acids are obtained. ... 

Scheme 207). Diazametallacycles such as 831 are key intermediates involved in imine metathesis catalyzed by zirconocene imido complexes,628 the authentic samples of which were synthesized independently by the reaction of 825 with 2 equiv. of the corresponding imine.629 The zirconocene imido complex 825 also ring-opens epoxides such as styrene oxide regioselectively to give metallacycle 832 (Scheme 207).630... 

C-substitution of nitrogen heterocycles , Vorbriiggen, H. and Maas, M., Heterocycles, 1988, 27, 2659 (discusses electrophilic and radical substitutions, lithiations and the use of iV-oxides) Regioselective substitution in aromatic six-membered nitrogen heterocycles , Comins, D. L. and O Connor, S., Adv. Heterocycl. Chem., 1988, 44, 199 (discusses electrophilic, nucleophilic and radical substitution, and metallation). 

For example, the three hydroxy groups of cholic acid in the 3-,7-, and 12-positions can all be oxidized regioselectively (Fig. 16.2-19) l83-85l. 

The N(l) atom of 3-aryl-l,2,4,5-tetrazines is oxidized regioselectively by methyl(trifluoro-methyl)dioxirane to give the hitherto unknown iV(l)-oxides (96T2377). 

Acetonitrile oxide regioselectively reacts with dialkylaminobutenones to form 5-acetyl-3-methylisoxazole (322) and a small amount of 4-acetyl-3-methyl-isoxazole (323) (92SC2902). 

A mild and efficient Pd(II)-catalyzed oxidative regioselective diarylating carbocyclization of dienynes was developed by using arylboronic acids with stereoselective formation of tetrahydrofurans and tetrahydropyrans (13CEJ6571). 

Regioselective oxidation of primary, secondary 1,4-dioIs with bromine and a nickel(ii) salt provides y-substituted butyrolactones in good yields. The tetrahydrofuran (104, R = Me) is also oxidized regioselectively with chromic anhydride to the lactone (105) in low yield, but the reaction has been used in the synthesis of compounds related to methylenomycin. However, the... 

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