Oxidation with ceric ammonium nitrat

The /7-nitrophenyl ether was used for the protection of the anomeric position of a pyranoside. It is installed using the Konigs-Knorr process and can be cleaved by hydrogenolysis (Pd/C, H2, AC2O), followed by oxidation with ceric ammonium nitrate (81-99% yield). ... 

Amide nitrogens can be protected by 4-methoxy or 2,4-dimethoxyphenyl groups. The protecting group can be removed by oxidation with ceric ammonium nitrate.243 2,4-Dimethoxybenzyl groups can be removed using anhydrous trifluoroacetic acid.244... 

Only a few examples exist for the intermolecular trapping of allyl radicals with alkenes68,69. The reaction of a-carbonyl allyl radical 28 with silyl enol ether 29 occurs exclusively at the less substituted allylic terminus to form, after oxidation with ceric ammonium nitrate (CAN) and desilylation of the adduct radical, product 30 (equation 14). Formation of terminal addition products with /ram-con figuration has been observed for reaction of 28 with other enol ethers as well. 

Unlike benzylic groups, they cannot be made directly from the alcohol. Instead, the phenoxy group must be introduced by a nucleophilic substitution.30 Mitsunobu conditions are frequently used.31 The PMP group can be cleaved by oxidation with ceric ammonium nitrate (CAN). 

Dihydropyrimidines are normally readily oxidized to the corresponding pyrimidines by dehydrogenation, hydrogen transfer, or disproportionation reactions <1994HC(52)1, 1996CHEC-II(6)93>. For example, the oxidation of a series of trifluoromethyl ketones 522 with DDQ occurred readily at room temperature <1997H(44)349>. Facile room temperature oxidation with ceric ammonium nitrate (CAN) has also been achieved <2003ARK(xv)22>. 

Cyclohexanone (202) was converted to compound (203) whose transformation to cyclohexanone (204) was accomplished in three steps. It underwent cyclialkylation with boron trifluoride etherate affording the cyclized product (205) (R=R,=OMe) in 64% yield along with naphthalene (206) (R=Ri= H,H). Compound (205) on heating under reflux with DDQ in benzene produced ketone (207) whose tosylhydrazone on treatment with sodium cyanoborohydride afforded reduced product (208). Deprotection of the aryl methyl ethers and oxidation with ceric ammonium nitrate led to the formation of miltirone (197). 

The Nicholas reaction was used to synthesize the p-lactam precursor of thienamycin in the laboratory of P.A. Jacobi and thereby accomplish its formal total synthesis. The necessary p-amino acid was prepared by the condensation of a boron enolate (derived from an acylated oxazolidinone) with the cobalt complex of an enantiopure propargylic ether. The resulting adduct was oxidized with ceric ammonium nitrate (CAN) to remove the cobalt protecting group from the triple bond, and the product was obtained with a 17 1 anti.syn selectivity and in good yield. 

The esters were prepared from the phenol and the acid chloride plus DM AP (or from the acid plus trifluoroacetic anhydride). In these esters the steric hulk of the ortho substituents protects the carhonyl from nucleophilic reagents, making them difficult hydrolyze. Although the diisopropyl derivative can be cleaved with hot aqueous NaOH, the di-f-butyl derivatives could only be cleaved with NaOMe in a mixture of toluene and HMPA. The related 2,6-di-f-butyl-4-methoxyphenyl ester can be cleaved oxidatively with ceric ammonium nitrate. These hindered esters have found utility in directing the aldol condensation. ... 

One vety useful transfomiation of these adducts is given in equation (75). Hydrolysis of the diester to the diacid, followed by bis>decarboxylation either by a double Curtius rearrangement or oxidatively with ceric ammonium nitrate, yields an unsaturated lactone. This overall sequence is equivalent to effecting a Diels-Alder reaction wiA carbon dioxide, which is unreactive as a dienophile. 

Suzuki-Miyaura coupling of D with I smoothly afforded J, which was oxidized with ceric ammonium nitrate to give K. For the final demethylation of K, several methods were tried without success treatment of K with boron tribromide, 47% hydrobromic acid, lithium chloride in DMF, trimethylsilyl iodide, and potassium thiophenolate in diethylene glycol. Finally, clean demethylation of K was achieved with aluminum chloride in dichloromethane at room temperature to give diospyrin (58) as orange plates. The proposed structure 58 was thus confirmed by its synthesis.130... 

Cycloaddition (5,647-648). The first step in a synthesis of (+)-2,3-dihydro-triquinacenone-2 (5) involves addition of TCNE to cyclooctatetraeneiron tricarbonyl (1) in a 1,3-bonding scheme. The yield is surprisingly high (96%). The iron atom is then extruded by oxidation with ceric ammonium nitrate (4, 72)... 

Reaction of 61 with ethylmagnesiiun chloride in THF at -78 °C was fully stereoselective yielding a single product that furnished hydroxyketone 58 after hydrolysis. Reduction of 58 with potassiiun borohydride gave a mixtine of diols in the ratio 15 2, from which a major isomer was isolated by column chromatography and oxidized with ceric ammonium nitrate (CAN) to quinone 62 in 40% overall yield (Scheme 13). 

Enantiomer selective coloration of optically active amines, our important project, was realized by chiral azophenol crown 4 incorporated with two units of optically active hydrobenzoin. The synthetic route is shown in Scheme 2. Reaction of 2,6-bis(bromomethyl)-l,4-dimethoxybenzene 22, which is derived from hy-droquinone monomethylether 19 by a three-step procedure, with the dibutyltin derivative 26 of optically active dihydrobenzoin gives optically active podand 23 in 63% yield. Cyclization of 23 with the ditosylate of polyethylene glycol, followed by oxidation with ceric ammonium nitrate (CAN) and treatment with dinitrophenylhy-drazine, affords the desired chiral azophenol crowns 4n. 

The synthesis of p-lactams unsubstituted on nitrogen also cannot be accomplished directly due to the instability of most imines derived from ammonia. However, imines derived from 4-methoxyaniline and 4-ethoxyaniline readily afford A/-aryl p-lactams cleavage of the A-aryl bond is accomplished by oxidation with ceric ammonium nitrate. A-Trimethylsilyl imines have also been used to provide NH P-lactams. ... 

As we saw in Section 11.17, cyclobutadiene is antiaromatic and exceedingly difficult to prepare and study. Its successful preparation by Rowland Pettit (University of Texas) in 1965 demonstrated how transition-metal organometallic cbemistry can provide access to novel reactions and structures. His approach was to prepare cyclobutadiene as a transition-metal complex, then destabilize the complex to trigger its dissociation. The sequence for cyclobutadiene begins with the reaction of cis-3,4-dichlorocyclobutene with diiron nonacarbonyl [Fe2(CO)9]. The resulting iron-cyclobutadiene complex satisfies the 18-electron rale, is stable, and undo-goes a variety of reactions. Most importantly, oxidation with ceric ammonium nitrate (a source of Ce ) lowers the electron count Irom 18 to 16, causing the complex to dissociate and Ubo-ate free cyclobutadiene. 

An alternative cyclization strategy toward dibromophake-Uin (44) was reported by Feldman [131]. Subjection of a thiolated dihydrooroidin derivative (200) to Pummerer conditions induced closure to tetracycle 201 (Scheme 13.35). Oxidation with ceric ammonium nitrate led to the cyclic urea-containing natural product dibromophakeUistatin (202), which could be converted to dibromophakeUin in two steps. This represents a complimentary PGF mode of closure to that developed by Buchi/Home (Scheme 13.7). Feldman is currently attempting to apply this strategy to the synthesis of the more complex PIAs such as palau amine (56) [132]. 

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