Ketones cerium ammonium nitrate

Despite the ionic reactions, other reactions (presented in Scheme 44) show that free-radical mechanisms can also take place. Catalyzed by ebselen, TBHP oxidation of alkylarenes to alkyl aryl ketones (141) [240], anthracene to anthraquinone (142), 1,4-dimethoxyarenes to 1,4-quinones (e.g., menadione 143) [244], and oxidative coupling of 2-aminophenol to phenoxazinone (144) [245] gave results similar to these when one-electron oxidants such as Ce(IV), Ag(II), or Mn(III) were the reagents. Moreover, oxidation of azine derived from 2-acetylpyridine gave a mixture of ketone (145) and condensed triazole (146) [240], The same result was found when cerium ammonium nitrate was used as the reagent. This suggests that the... 

The products were readily converted to free 8-amino ketones and esters. Thus, treatment of the products with cerium ammonium nitrate in acetonitrile-water (9 1) at room temperature induced smooth deprotection of the 2-methoxyphenylamino group to give free /5-amino carbonyl compounds [71,72]. 

Preparation of a-fluoro ketones or aldehydes can also be achieved by cerium ammonium nitrate oxidation of the corresponding silyl nitronates. C-acylation compounds derived from nitroalkanes can be... 

Reductive amination combines an in situ imine formation with a consecutive reduction. If this reduction is carried out in an asymmetric fashion, chiral amines are accessible in one step from the corresponding ketones (Scheme 32.20, route A). Primary amines are available via the p-methoxy-phenyl (PMP)-group that can be removed with cerium ammonium nitrate (CAN) afterward (route B). 

Selective oxidation of methyl pyrroles 65 possessing an a-carboxylic ester and sensitive p-substituents can be accomplished using cerium triflate in methanol <96TL315>. Moreover, the resultant a-methoxymethylpyrroles 66 may be converted to dipyrrylmethanes 67 in a "one-pot" sequence by treatment with 48% HBr. The dipyrrylmethanes, in turn, can be further oxidized to dipyrryl ketones by ceric ammonium nitrate <96JHC221>. 

Cerium(IV) ammonium nitrate (CAN) has been reported to catalyse a facile and efficient aza-Michael addition of aromatic and aliphatic amines to a -unsaturated esters in the absence of solvent under ultrasound irradiation.136 a,/l-Unsaturated ketones react in aqueous solutions under these conditions but only with aliphatic (not aromatic) amines.137... 

Primary benzylic alcohols (equation 10) can be oxidized in the presence of saturated primary alcohtris using a catalyst derived from ammonium cerium(IV) nitrate supported on charcoal with air as the cooxidant (under these conditions a-hydroxy ketones are oxidized to a-diketones). ... 

Treatment of triisopropylsilyl enol ethers of cyclic ketones with ammonium cerium nitrate (3 equiv) and sodium azide (4.5 equiv) in acetonitrile at — 20 °C gave a-azido ketones in good yields124. By varying the ratio of the reagents the yields were lower or the formation of byproducts, difficult to separate, increased. Mixture of diastereomers (ratio not reported) were generally obtained from substituted substrates, except from the bicyclic ketones 16. 

The regioselective oxidation of aziridines to a-tosylamino ketones has been accomplished via NBS and cerium(iv) ammonium nitrate (CAN) <2005TL4111>. Both styryl aziridines, 388, and aliphatic aziridines, 390, have been oxidized. A related report uses /3-CDs in addition to NBS to catalyze the same transformation <2005TL1299>. These reaction conditions also work well for epoxides to provide the corresponding a-hydroxy ketones (Scheme 99). 

Sodium Azide/Ammonium Cerium(IV) Nitrate. Silyl enol ethers give a-azido ketones on treament with sodium azide and anhydrous ammonium cerium(IV) nitrate in anhydrous acetonitrile (see Eq. 97).297 325 33i With a glycal, the 2-azido-1-hydroxy nitrate derivative is formed.332 Low yields due to hydrolysis of the silyl enol ether may be improved by use of the triisopropylsilyl (TIPS) derivatives,331 although with a sterically encumbered taxane-derived enol ether the TMS derivative gives higher yields than the TIPS derivative.325 The mechanism is believed to involve addition of an azide radical to the double bond. 

Pyrroles which have a ketone or ester substituent are more resistant to ring degradation and high-yielding side-chain oxidation can be achieved using cerium(IV) ammonium nitrate, with selectivity for an a-alkyl. ... 

The advantage of mild reaction conditions is obvious, if enolates are oxidized at low temperatures in methanol. Thus, Narasaka et al. demonstrated that cerium(IV) ammonium nitrate smoothly generates radicals 12 after deprotonation of nitro compounds Id [8], The electrophilic radicals can be added to electron-rich double bonds like silyl enol ethers 13. Ketones 14 are formed as intermediates, which after elimination of HNO2 under the basic reaction conditions alford enones 15 in high yields as final products (Scheme 4). 

Finally, cerium(IV) ammonium nitrate can serve as the radical source by itself, generating NO3 radicals If by photolysis. The addition of such radicals to cyclo-alkynes 20 initiates an interesting tandem reaction [12]. Transannular hydrogen atom abstraction by the vinyl radical 21 affords the intermediate 22, which undergoes a 5-exo cyclization to the radical 23. In the last step, the ketone 24 is formed by elimination of NO2 in moderate yield thus, the overall sequence can be described as a self-terminating radical reaction (Scheme 7). 

Oxidation and Bromination of Other Functional Groups. Selective oxidation of alcohols may be achieved using a 1 1 complex of NBS and tetrabutylammonium iodide, whereas 1,2-diols are converted into 1,2-diketones using iV-bromosuccini-mide. An efficient and mild procedure has been reported for the preparation of benzoic acids via oxidation of aromatic carbonyl compounds by employing NBS and mercuric acetate. Selective and efficient oxidation of sulfides to sulfoxides has been achieved with NBS in the presence of /3-cyclodextrin in water. Epoxides and aziridines are conveniently oxidized to the corresponding a-hydroxy or Q -amino ketones using cerium(IV) ammonium nitrate and NBS. ... 

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