O-Chloranil oxidation with

Some 2-aminopyridine derivatives (107 and 108) were formed, also. Of the Schiff bases, only the benzaldehyde derivative reacted, yielding the 4-hydroxypyrido[l,2-a]pyrimidine (109), which was then oxidized with o-chloranil to the 4-oxo compound. 

Sessler and coworkers have also developed a 3 -I- 2 approach to meso-diarylsapphyrins. This strategy, which is based on those used by Ogoshi and Smith ° to generate mc50-arylporphyrins, is outlined in Scheme 5.2.5. It involves the acid-catalyzed condensation of the diol 5.48 with the diacid tripyrrane 5.14. After oxidation with o-chloranil and chromatographic workup, diphenylsapphyrin 5.49 was obtained in ca. 3% yield. While less direct than the one-pot approach to 10,15-diarylsapphyrins outlined earlier (Schemes 5.1.6 and 5.1.7), this strategy allows synthetic access to isomeric 5,20-substituted diarylsapphyrins (e.g., 5.49). 

Benz[a]acridine is reduced by lithium in liquid ammonia to the 1,4,7,12-tetrahydro derivative, m.p. 177°C (M, Schaefer Ridder and U. Engelhardt, J. org. Chem.. 1981, 46, 2895). Oxidation with o-chloranil gives 1,4-... 

Figure 1. Mossbauer spectrum of polyferrocenylmethyl acrylate oxidized with o-chloranil (adapted from reference 17).

Pd2(dba)3/l,4-bis(diphenylphosphino)butane (DPPB) in the presence of 2-mercaptobenzoic acid <95TL1267>. The Af-allylindolines can be easily oxidized to the corresponding indoles at room temperature with o-chloranil. Additionally, Al-allylanilines were also found to undergo aromatic 3-aza-Cope rearrangements in the presence of Zeolite catalysts to give indoline derivatives as the major product <96TL5281>. 

An alternative new synthetic approach to chrysene 1,2-dihydro-diol based on Method IV has recently been developed (60). This method (Figure 12) entails synthesis of 2-chrysenol via alkylation of 1-1ithio-2,5-dimethoxy-1,4-cyclohexadiene with 2-(1-naphthyl) e-thyl bromide followed by mild acid treatment to ge nerate the diketone 12. Acid-catalyzed cyclization of 12 gave the unsaturated tetracyclic ketone 13 which was transformed to 2-chrysenol via dehydrogenation of its enol acetate with o-chloranil followed by hydrolysis. Oxidation of 2-chrysenol with Fremy s salt gave chrysene... 

Ether cleavage of 4-heptyl-3-methylveratrole 121 using boron tribromide affords 4-heptyl-3-methylcatechol 122 (Scheme 38). Oxidation of the catechol 122 with o-chloranil to 4-heptyl-3-methyl-l,2-benzoquinone 123 and subsequent immediate addition of aniline leads to 5-anilino-4-heptyl-3-methyl-l,2-benzo-quinone 124. Unlike the very labile disubstituted ort/zo-quinone 123, compound 124 is stable and can be isolated. Palladium(II)-mediated oxidative cyclization of the anilino-l,2-benzoquinone 124 provides carbazoquinocin C 51. 

Scheme 22)87 The intramolecular 4 + 2-cycloaddition of ynamides with conjugated enynes produces substituted indolines that can be oxidized to indoles with o-chloranil.88 The double Diels-Alder cycloaddition of the linear conjugated tetraene... 

The oxidation of compound (233) with o-chloranil in CHC13 gave the benzodioxane adduct (234) along with a minor amount of the desired product (235). Extended treatment with o-chloranil or reaction of adduct (234) with o-chloranil gave compound (236) (Scheme 22) (79JOC2518). 

Nucleophilic addition of 1005 to an 7V-acyliminium ion, e.g., a Reissert salt, and oxidation of the resulting adduct affords a 2-(heteroaryl)oxazole 1019. Acylation of a nitrogen heterocycle 1016 with ethyl chloroformate generated the intermediate Reissert salts 1017 in situ (Scheme 1.272). Addition of 1005 to 1017 gave adducts 1018, which produced 1019 after oxidative deacylation with o-chloranil. Examples of 2-(heteroaryl)oxazoles prepared from thiazole, benzothia-zole, pyridine, quinoline, and isoquinoUne are shown in Table 1.77. Donodni and co-workers summarized their early work on preparation and reaction of 2-(trimethylstannyl)oxazoles and 2-(trimethylsilyl)oxazoles. 

Dehydrogenation of Carbonyl Compounds. Oxidation of thioflavanones gave thioflavones in excellent yield whereas dehydrogenation with o-chloranil under like conditions failed (eq 27). Inductive effects play an important role in such dehydrogenations. For example, the sulfone analog resisted dehydrogenation whereas the sulfoxide derivative gave the thioaurone product in low yield. 

A simple indoline (and hence indole) synthesis features a Parham cyclization, e.g., 47—>48, and this has been extended to an enantioselective 3-substituted indoline synthesis, i.e., 49 +50. Oxidation of indolines 48 with o-chloranil affords the corresponding indoles in good yield." Related enantioselective indane construction has been described... 

Cyclo-octatetraene monoepoxide reacts with 3,6-diphenyl-sym-tetrazine to give the ring-expanded (214) which is oxidized by o-chloranil to give 1,4-diphenyloxonino [4,5-c/]pyridazine. The nature of the products obtained from cyclo-octatetraene... 

Alternatively, similar amino acid derivatives (54) can be obtained by oxidation of the oxazolines with o-chloranil and reaction of the adducts with nucleophiles (555). 

Tricarbonyl[t/M-(ethoxycarbonyl)-l//-azepine]iron(0) (30) with the 2-oxyallyl cation derived from 2,4-dibromo-2,4-dimethylpentan-3-one and nonacarbonyldiiron(O) yields a mixture of adducts which, after oxidative decomplexation with tetrachloro-l,2-benzoquinone (o-chloranil), affords the tetrahydrofuro[2,3-A)azcpine derivative 33 and the 3-substituted 1H-azepine-l-carboxylate 34.227... 

Phosphorus heterocycles 246 derived from hydroxyphenyl benzimidazole and aminophenyl benzimidazole undergo oxidative cycloaddition with 3,5-di-/fV/-butyl-l, 2-bcnzoquinonc to give a mixture of 247 and 248 (Equation 60) <2004HAC307, 2004HAC321>. Oxidative addition of ort o-chloranil to bis- and tetrakis-cyclodiphos-phazene compounds gives bis- and tetrakis-spirophosphoranes, for example, 41 (Equation 61). 

In contrast, 1-methoxy- (or ethoxy-) carbonyl-l//-azepine-tricarbonyliron complex with the tetrazine diester undergoes unprecedented [2+4]7t cycloaddition at the C-2—C-3 azepine double bond to give, after loss of nitrogen and decomplexation and dehydrogenation using o-chloranil or trimethylamine N-oxide, the isomeric pyridazino[4,5-6]azepine system (82JOC110). Similar adducts are also obtained with tetrachlorothiophene 1,1-dioxide. 

Several attempts have been made, especially in recent years, to oxidize saturated to unsaturated azlactones. 64 The oxidation of saturated azlactone 13 with DDQ or o-chloranil in the presence of collidine as a weak base affords the unsaturated azlactone 14 in 40-50% yield (Scheme 5). Breitholle and Stammer 65 reported the preparation of unsaturated azlactone 16 by dehydrobromination of the bromopseudoazlactone 15 (Scheme 5). The pseudoazlactones derived from Ala and Abu tend to dibrominate, but careful reaction conditions allowed their isolation in acceptable yields. 65 This procedure is applicable to the preparation of derivatives of AAla, AAbu, AVal, and ALeu. 66 ... 

As early as in 1956, Braude et al.92 suggested that the selective oxidation of unsaturated alcohols with the quinone o-chloranil (82), can be explained by the intermediacy of a resonance-stabilized cation resulting from a hydride abstraction. Later, detailed mechanistic studies confirmed this hypothesis94c,95e in oxidations performed with the more common quinone DDQ. 

The mode of reaction of fulvenes with o-quinones varies with structure. As illustrated below, 7,7-disubstituted fulvenes (91) react with o-benzoquinone and alkyl substituted o-quinones to give bridged diones 90,91) (92). The regiochemistry of these reactions was determined by photobisdecarbonylation to 93. Subsequent oxidation with chloranil provided a synthesis of benzofulvenes (94). 

Harima et al. (1989) measured the photogeneration efficiencies of 5,10,15,20-tetraphenylporphyrin (TPP) and its Zn complex (ZnTPP) doped with tetracyano-quinodimethane (TCNQ), o-chloranil (Chi), phenothiazine (Pz), and I. TCNQ, Chi, and I are electron acceptors while Pz is a donor. The porphyrins were selected on the basis of differences in exciton diffusion lengths (Tanimura et al., 1980 Yamashita et al., 1987) and oxidation potentials (Felton, 1978). The photogeneration of I doped ZnTPP was described by a direct ionization process via a singlet state of ZnTPP and ascribed to a reduction of the electron-hole recombination rate in the depletion layer. For TPP doped with Chi, Pz, or I, the results were explained by exciplex dissociation (Loutfy and Menzel, 1980). For... 

Attempts have been made to realize experimentally the conversion of laudanosine-type bases to bases of the aporphine and morphine series, so far without success. In an attempt to convert laudanosoline [xtx] to norglaucine [x ] it was discovered that the former is very readily oxidized to intractable materials, but that oxidation with chloranil [5-6] or tetrabromo-o-benzoquinone [7] affords, not the expected norglaucine, but 2 3 11 12-tetrahydro-8-methyldibenzotetrahydropyrrocolinium ohloride [xxi]. Protosinomenine [i] has been synthesized in two ways [3, 8], but the conditions required for the conversion of this base to sinomenine [iv] have not yet been realized and their discovery must be largely fortuitous [6],... 

The base-catalyzed cyclization of ethyl 3-[alkyl(4-cyanopyridazin-3-yl)amino]propanoates gives ethyl 8-alkyl-5-amino-7,8-dihydropyridazine-6-carboxylates 1, which by acidic hydrolysis were converted to the corresponding ends 2. Due to their air sensitivity, ends 2 are partly converted into ethyl 8-alkyl-5-oxo-5,8-dihydiopyiido[2,3-c]pyridazine-6-carboxylates 3. To avoid mixtures, the oxidation is completed by treatment with tetrachloro-l,2-benzoquinone (o-chloranil).20... 

A general synthesis of quinazoline 1,3-dioxides and their 1,2-dihydro derivatives was devised by Taylor and Bartulin. In this synthesis o-hydroxyl-aminobenzaldehyde oxime condensed with aldehydes and ketones to yield 2,2-disubstituted 1,2-dihydro-l-hydroxyquinazoline 3-oxides (63). When the dihydro compounds (63 R1 = H) derived from aldehydes or from formaldehyde were oxidized with chloranil, benzoquinone, or mercuric oxide, 2-substituted quinazoline 1,3-dioxides (64) and the parent quinazoline 1,3-dioxide (63 R = H) were produced.173... 

In 2011, Itami and Studer [183] developed a palladium-catalyzed C4-selective arylation of thiophenes and thiazoles with arylboronic acids. Although they had already reported the C4(/J)-selective arylation of thiophenes with aryl iodides [88] (Scheme 17.18), this C-H/C-B coupling method [using a Pd"/hipy or phen/TEMPO ((2,2,6,6-tetramethylpiperidin-l-yl)oxyl) catalyst system] enabled the use of thiazoles as aryl nucleophiles. They also applied this coupling reaction to the synthesis of the core structure of SCH-785532, which is known as a BACE inhibitor. In the same year, Itami [184] reported a direct arylation of a PAH with arylboronic acids to generate a 7t-expanded PAH. Treatment of pyrene 142 with arylboroxine 143 in the presence of Pd(OAc)2 and o-chloranil as an oxidant, followed by cydiza-tion under stoichiometric FeClj, produced PAH 144. Key to the unprecedented C-H arylation was a notable combination of Pd" and o-chloranil. 

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