Cerium ammonium nitrate-Silica

Moore et al. investigated the thermal rearrangements of differently substituted cyclobutenones. Reactions of 4-alkenyl-4-hydroxycyclobute-nones such as 18, in which the triple bond is replaced by a double bound, are complementary to the ring expansions of 4-alkynyl-4-hydroxycyclobute-nones and provide a route to the differently substituted benzoquinones, such as aurrantiogliocladin 19. The reaction proceeds via enyne-ketene 20. Since cyclization produces a derivative of hydroquinone 21, an additional oxidation step is required that is accomplished with the use of cerium ammonium nitrate on silica. This ring expansion process is independent of the... 

To a reaction tube charged with cerium ammonium nitrate (68 mg, 0.125 mmol, 0.25 mmol of NH4, 1 equiv.) and copper trifluoroacetate hydrate (14.5 mg, 0.05 mmol, 20 mol%) was added a solution of acetaldehyde (1 mmol) and H2O (135 iL, 7.5 mmol, 30 equiv.) in DMF (3 mL) imder argon (1 atm). The reaction mixture was then stirred at 80°C for 12 h. After cooling to room temperature, the mixture was diluted with ethyl acetate, washed with saturated sodium bicarbonate, water and brine, dried over anhydrous sodium sulfate, and concentrated in vacuo to give dark residue, which was purified by flash chromatography (using petroleum ether and ethyl acetate as the effluent) on silica gel to afford the 5-diarylpyridine product. 

Mononitration of 1-hydroxynaphthalene could be obtained by use of ammonium hexanitra-tocerate(IV) supported on silica gel in acetonitrile (Chawla and Mittal, 1985) (scheme 39). The same reaction with CAN in acetic acid give the 2,4- and 4,6-dinitro derivatives. By the same method, 2-hydroxy naphthalene is converted into l-nitro-2-hydroxy naphthalene and 4-nitro-2-hydroxynaphthalene (scheme 40). The 1-alkoxynaphthalenes can be mononitrated regioselectively in the 4-position (scheme 41). The lower reactivity of CAN supported on silica gel is also evident from the fact that naphthalene derivatives are not oxidized into 1,4-naphthoquinones. The authors noticed that no reaction could be observed when ammonium hexanitratocerate(IV) was replaced by a mixture of ammonium nitrate and ammonium cerium(IV) nitrate. Silica supported CAN has also been used for the nitration of methoxyben-zenes (Grenier et al., 1999) and less electron rich aromatic compounds like benzene, toluene, chlorobenzene and bromobenzene (Mellor et al., 2000) (scheme 42). For the less electron rich aromatics, dichloromethane is used as solvent instead of acetonitrile. In most cases, the yields are good to excellent. 

Nitration of naphthalene by use of cerium(IV) ammonium nitrate suspended on silica gel, or in homogeneous solution, in the presence of alcohols, sodium or tetrabutylammonium nitrite and acid gives mainly l-alkoxy-4-nitronaphthalenes together with some of the 2-nitro isomers.34 The results are consistent with initial attack by N02- alone or complexed with cerium(IV) ion at the 1- and 2-positions in a ratio of 5 1. 

Catechols and hydroquinones can be converted (91-98%) into quinones by cerium(IV) salts coated onto silica as free-flowing yellow powder from impregnation with cerium(IV) ammonium nitrate. This reaction is usually performed in the presence of magnesium sulfate. The same (NH4)2Ce(N03)6 SiQ2 reagent in the dry state effects oxidative nitrations of arenes. For example a-mq>hthol is converted to the Orth) (42%) and the para (38%) nitro compounds, while its metiiyl or ethyl ethers give exclusively the para nitration product (equation 4). In solution, the products are cmtaminated with the products of dinitration and of oxidation into quinones. ... 

Silica gel supported cerium(IV) ammonium nitrate (CAN) has been employed for controlled nitration of some naphthalene derivatives. While treatment of hydroxynaphthalenes and polynuclear arenes with cerium(IV) ammonium nitrate absorbed on silica gel without a solvent affords mononitro derivatives, the reaction of the same substrates with cerium(IV) ammonium nitrate in solution alfords a considerable per-... 

To a cold (0 "C), magnetically stirred solution of 4,4-dimethyl-3,5-diphenyl-3i/-pyrazole (2.4 g, 10 mmol) and cyclobutadieneirontricarbonyl (1.92 g, 10 mmol) in acetone (125 mL) under Nj was added ceric ammonium nitrate (27.4 g, 50 mmol) in portions over 30 min. The resultant slurry was poured into anhyd EtjO and the precipitated cerium salts were removed by filtration. The filtrates from two identical runs were evaporated and the combined crude product chromatographed (silica gel, EtjO/hexane 1 9). Recrystallization (hexane) gave 7,8-diaza-eui7o-9,9-dimethyl-l,6-diphenyltricyclo[4.2.1.0 ]nona-3,7-diene(9) as white crystals yield 4.09 g (68%) mp 153-154 "C (dec.). A solution of the diazene 9 (100 mg, 0.33 mmol) in EtjO (2 mL) was irradiated for 3 h with a 200-W Hanovia lamp (Pyrex filter). The progress of the reaction was monitored by TLC. Removal of the solvent gave 10 yield 90 mg (100%) mp 65-67 C. 

Naphthol (378, 0.36 g, 2.5 mmol) was dissolved in methanol (20 ml) at room temperature. Nitrogen was bubbled through the solution, into which ammonium cerium(lV) nitrate (1.39 g, 2.53 mmol) in methanol (15 ml) was added with stirring until the mixture turned reddish. The mixture was evaporated in vacuo and the residue was poured into water (100 ml) at 0 C and filtered. The cmde product was purified by silica gel chromatography using a petroleum ether / diethyl ether (3 1) as an eluent to afford 329 mg (92%) of pure l,r-binaphthyl-2,2 -diol (4) as a white crystalHne solid, m.p. 215 °C. 

Silica-gel-supported cerium(IV) ammonium nitrate has been... 

A good number of alternative methods are also available in literature for the synthesis of 1,5-benzodiazepine derivatives involving the use of a variety of catalysts such magnesium oxide/ phosphorus oxychloride (MOPO) [1], ionic liquid (1,3-di-n-butylimidazolium bromide) [2], silica gel-supported cerium(lll) chloride/sodium iodide [3], Sc(OTf)3 [4], InCls [5], InBr3 [6], ceric ammonium nitrate (CAN) [7], 2,4,6-trichloro-l,3,5-triazine (TCT) [8,9], GaCl3 [10], and Zr0C2-8H20 [11] in the presence or absence of solvent(s) at room temperature. 

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