Cerium ammonium nitrate CAN

Dihydropyrans [71] and 4-dihydropyranones [72] have been prepared by BF3 or Me2AlCl catalyzed Diels-Alder reactions of alkyl and aryl aldehydes with dienes 72 and 73 (Equations 3.20 and 3.21). Allylic bis-silanes are useful building blocks for synthesizing molecules of biological interest [73], 4-Pyra-nones have been obtained by cerium ammonium nitrate (CAN) oxidation of the cycloadducts. 

A similar process can be performed with the use of cerium ammonium nitrate (CAN) for generation of radicals from another CH acid, viz., methyl nitroacetate (72b) (Scheme 3.22, Eq. 2). 

Treatment of the 3,l-benzoxazin-2-one derivative 249 with cerium ammonium nitrate (CAN) resulted in removal of the /i-methoxybenzyl substituent, by oxidation of its a-position, which led to the human immunodeficiency vims-1 (HIV-1) reverse transcriptase inhibitor efavirenz 250 and anisaldehyde (Equation 24) <1998JOC8536>. 

In particular, A-arylsuccinimidate 62 (obtained from anizidine in three steps) with t-BuOK in THF produces the corresponding carbanion, which instantly cyclizes into crH-adduct 63. The latter, on oxidation with cerium ammonium nitrate (CAN) gives lactame 64 in 53% yield (Scheme 19). 

Thioamides of 3-oxoacids 118 are transformed into 1,2,4-dithiazolidines 29 by treatment with cerium ammonium nitrate (CAN) in MeOH or with CF3SC1 in CH2CI2 (Equation 16) <1996SC4165, 2001SC189>. The thermal conversion of 6/7-1,3,5-oxathiazine A-oxides 119 in refluxing benzene results in 1,2,4-oxathiazolines 20 with extrusion of R CHO. This reaction involves the heterodiene intermediate 120, which can be independently trapped by the reaction with EtOH (Scheme 32) <2003TL2517, 2004HAC175>. 

The C-Si bond of an SMA can also be cleaved by oxidizing reagents like cerium ammonium nitrate (CAN). Starting from (V-bis(trimethylsilyl)methylazetidinones, treatment with CAN probably leads to the oxidation product of the two C-Si bonds, i.e., the corresponding disilylketal that is hydrolyzed into the formamide to give the N-H azetidinones (yields >80%). This constitutes an alternate and more efficient way to sequential fluoride-induced desilylation. Peterson olefination, ozonolysis, and formamide decomposition when deprotection of bis(trimethylsilyl)methylated azetidinones into NH-azetidinones is required.228,230... 

The direct oxidation of arenes to quinones is a reaction with a limited scope [41], Only substrates that form stable quinones give good yields. For example, oxidation of anthracene to stable 9,10-anthraquinone with chromic acid is practiced on industrial scale. Such oxidations are believed to proceed through a series of one-electron oxidation/solvolysis steps. Yields and selectivity may be improved by using a strong one-electron oxidant such as cerium ammonium nitrate (CAN), as in the oxidation of phenanthrene to phenanthrenequinones (Eq. 9) [42]. 

PMB ethers can be cleaved oxidatively with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)11 in dichloromethane/water tor with cerium ammonium nitrate (CAN) in acetonitrile/water.12 Many other protecting groups such as esters, isopropylidene acetals, benzyl ethers, allyl ethers and f-butyldiphenyl silyl (TBDMS) ethers are stable to these conditions (Scheme 2.4). The cleavage reaction, with DDQ is initiated with a single-... 

One-electron oxidation of the p-allyloxy nitroalkane (85) by cerium ammonium nitrate (CAN) produces a tetrahydrofuran derivative (86) (eq. 3.31). 

Two short syntheses of P-lapachone from readily available naphthols and 3-methylbut-2-enal via a mild phenyl-boronic acid mediated cyclization to 2//-chromenes have been reported. Catalytic hydrogenation of 2H-chromenes with H /Pd-C in ethyl acetate afforded the corresponding naturally occurring chromanes (72) and (73). Oxidation of the adequate chromane with an excess of cerium ammonium nitrate (CAN) furnished P-lapachone in 62% yield [153]. 

JOC6261> and peptide isosteres <1995JOC8074>. The A, A -diprotected phenylalaninal 465 (Scheme 119) was obtained from L-phenylalanine 464 in good yield. The reaction of 465 with 2-TST provided the expected a -amino alcohol 466 as a major product. The oxidative removal of the -methoxybenzyl group with cerium ammonium nitrate (CAN, (NH4)2Ce(N03)6) and silylation furnished the compound 467, which was transformed into the aldehyde 468 in excellent yield. 

The products were readily converted to free ff-amino ketones and esters. Thus, treatment of the products with cerium ammonium nitrate (CAN) in acetonitrile-water (9 1) at room temperature induced smooth deprotection of the 2-methoxy-phenylamino group to give the corresponding free yS-amino carbonyl compounds (Eq.(14.5)) [50, 51]. 

Pummerer-like cyclization reactions were utilized to prepare spirocyclic oxindole derivatives <04OL1869, 04OL2849>. For example, treatment of 2-sulfenylindole 215 with an iodonium reagent in the presence of 2,6-lutidine produced thioimidate 216. Oxidation of the latter with cerium ammonium nitrate (CAN) gave spirooxindole 217. 

The aromatization of dihydro heterocycles was carried out using cerium ammonium nitrate (CAN) at ambient temperature and results in trifluoromethylated heterocycles in 18-68% yield (Fig. 7.32). While trifluoromethylation of 3-picoline is regioselective giving 5-methyl isomer in 41 % yield, the reaction of other 3-substituted pyridines leads to the mixture of — 3 and — 5 regioisomers. 

An efficient method (55-80% yields) gave 3-substituted carbostyrilqui-none derivatives 52 from 5,8-dialkoxyquinolines followed by a cerium ammonium nitrate (CAN) oxidative demethylation (Figure 2) (93H(36) 1387). The synthesis of more complex analogs of 52 is presented in Scheme 18. 

A round-bottomed flask was charged with 53 mg 8,16-dibut-3-enyl-l,9-dioxa-cyclohexadeca-6,14-diyne-2,10-dione hexacarbonyl dicobalt complex (0.0534 mmol) and 12 mL acetone to yield a red suspension. The reaction flask was cooled at 0°C, and 472 mg cerium ammonium nitrate (CAN) (0.86 mmol) was added in eight portions (59 mg/portion) over 5 min. The cooling bath was removed, and the reaction was allowed to stir at room... 

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