Aldehydes cerium ammonium nitrate

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. 

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. 

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... 

Selective oxidation of methyl groups can be achieved by platinum salts in aqueous solution. Thus, p-toluenesulfonic acid is oxidized to the alcohol and then to the aldehyde by the Pt(II)/Pt(IV) system. Likewise the methyl group of ethanol can be oxidized without affecting the hydroxyl group [208]. Potassium or sodium bromate in the presence of cerium ammonium nitrate in a water/di-oxane (2 3) mixture can oxidize toluene into a 1 1 mixture of benzaldehyde and benzoic acid. Ethylbenzenes yielded acetophenones [209]. 

Different from the hydroxyalkylation reactions using carbonyl compounds as substrates, Nicolaou s and Macmillan s groups developed independently the intramolecular asymmetric Friedel-Crafts-type a-arylation of aldehydes with electron-enriched arenes based on the SOMO activation strategy. Using chiral imidazolidione as catalyst, a series of cyclic aldehydes were obtained in good yields and enantioselectivities with cerium ammonium nitrate (CAN) as single electron transfer oxidant [46]. 

Keywords Aromatic aldehydes, amines, p-keto esters, cerium ammonium nitrate (CAN), homogeneous catalysis, acetonitrile, room temperature, one-pot synthesis, multicomponent reaction (MCR), tetrahydropyridines... 

SOMO catalysis, which has been the subject of considerable attention in recent years, is a unique and versatile activation mode that can participate in bond construction with various n-rich nucleophiles. The first asymmetric intramolecular a-arylation of aldehydes was reported by Nicolaou in 2009 using organo-SOMO catalysis [17a]. The authors applied imidazolidinone 23 as catalyst and cerium ammonium nitrate (CAN) as the oxidant Various 5-oxopentylbenzenes 36, or indole derivatives 38, could furnish the cyclic products 37 or 39, respectively, in good yields and with excellent ees (Scheme 36.11). Later, MacMillan disclosed similar research [17b], and a theoretical study of the intramolecular a-arylation of aldehydes was also reported by the same group via density functional theory [17c],... 

The use of cerium(IV) ammonium nitrate (CAN) as a catalyst for an aza-Diels-Alder reaction was reported in two different publications. In one report Perumal and co-workers react a variety of anilines 86 and aldehydes 87 with enamine 88 in the presence of 5 mol% CAN to form a series of tetrahydroquinolines 89. The reactions were performed at room temperature with very short reaction times and in good yields. In addition, the resulting tetrahydroquinolines could be oxidized to the corresponding substituted quinolines using 2.5 eq of CAN in high yields <06TL3589>. 

More recently, Menendez et al. reported a closely related four-component access to tetrahydropyridines, the amino alcohol being replaced by a primary amine and an alcohol. Thus, the cerium(IV) ammonium nitrate (CAN)-catalyzed reaction between primary aliphatic amines, 1,3-dicarbonyls, cx,p-unsaturated aldehydes, and alcohols resulted in the formation of 6-aUcoxy-2-methyl-l,4,5,6-tetrahydropyridines with... 

In 2007, MacMillan and co-workers reported conceptually novel reactions employing MacMillan s catalyst 5b [39]. This catalyst worked as a singly occupied molecular orbital (SOMO) catalyst in the presence of cerium (IV) ammonium nitrate (CAN) as a single-electron oxidant and the enantioselective a-allylation of aldehydes... 

Diverse dihydronaphtho[l,2-(r]furans were generated fix)m 1,4-naphthoquinones and olefins in the presence of ceric ammonium nitrate (13OBC6097). ( )-Lantalucratins A and B were produced in the presence of diammonium cerium(IV) nitrate (13T10470).Benzo[(>]furan moieties were synthesized by a three-component Mannich reaction of 3-acetyl-2H-chromen-2-one or l-(l-benzo[fc]fioran-2-yl) ethanone with p-substituted aromatic aldehydes and aromatic amines with ceric ammonium nitrate (CAN) as a catalyst (13MCR4787).p-Alkenylphenols went through the oxidative dimerization to generate substituted dihydrobenzo[l)]furans in the presence of CAN (13T653). 

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