Cycloheptatriene oxidation

Although the chemistry of zirconium in its lower oxidation states is still relatively unexplored, it is developing. Examples which offer the possibility of further exploitation include the blue, paramagnetic zirconium(III) compound 32) [L2Zr(/r-Cl)2ZrL2] L = C5H3(SiMe3)2-l,3, and the sandwich and half-sandwich compounds derived from cycloheptatriene red... 

Dibenzo[a,dlcyclohepta-1,4-diene-5-one Amitriptylin oxide Dibenzo[a,el cycloheptatrien-5-one Cyproheptadine 5H-Dibenzo (a,d 1 cycloheptene Protriptyline... 

Oxepin and its derivatives have attracted attention for several reasons. Oxepin is closely related to cycloheptatriene and its aza analog azepine and it is a potential antiaromatic system with 871-elcctrons. Oxepin can undergo valence isomerization to benzene oxide, and the isomeric benzene oxide is the first step in the metabolic oxidation of aromatic compounds by the enzyme monooxygenase. 

Three decades ago the preparation of oxepin represented a considerable synthetic challenge. The theoretical impetus for these efforts was the consideration that oxepin can be regarded as an analog of cyclooctatetraene in the same sense that furan is an analog of benzene. The possibility of such an electronic relationship was supported by molecular orbital calculations suggesting that oxepin might possess a certain amount of aromatic character, despite the fact that it appears to violate the [4n + 2] requirement for aromaticity. By analogy with the closely related cycloheptatriene/norcaradiene system, it was also postulated that oxepin represents a valence tautomer of benzene oxide. Other isomers of oxepin are 7-oxanorbornadiene and 3-oxaquadricyclane.1 Both have been shown to isomerize to oxepin and benzene oxide, respectively (see Section 1.1.2.1.). 

Phosphorus pentachloride, for conversion of pentaacetylgluconic add to add chloride, 41, 80 for oxidation of cycloheptatriene to tropylium fluoborate, 43, 101 with cyanoacetic acid, 41, 5 Phosphorus tribromide, reaction with 1.5-hexadien-3-ol, 41, 50 Phthalic anhydride, reaction with L-phenylalanine to yield N-phthalyl-L-phenylalanine, 40, 82 Phthalic monoperacid, 42, 77 N-Phthalyl-i.-alanine, 40, 84 N-Phthalyl-/3-alanine, 40, 84 N-Phthalylglycine, 40, 84 N-Phthalyl-l-/5-phenylalanine, 40, 82... 

The molecules taking part in a valence tautomerization need not be equivalent. Thus, NMR spectra indicate that a true valence tautomerization exists at room temperature between the cycloheptatriene 110 and the norcaradiene (111). In this case one isomer (111) has the cw-l,2-divinylcyclopropane structure, while the other does not. In an analogous interconversion, benzene oxide and oxepin exist in a tautomeric equilibrium at room temperature. 

The reaction of hexafluoroacetone azine with cycloheptatriene at 70 °C provides after 8 days a mixture containing 28% of unchanged azine 290 and products formed by three distinct mechanistic pathways, that is, criss-cross cycloaddition product 294, a bis-ene adduct 295 and its oxidation product 296, and [3+6] cycloaddition leading to diaziridine 297, in the ratio 15 38 7 (Scheme 40) <1995JFC(73)203>. 

The methodology employed for the oxidation of cycloheptatriene is based on an original report by Radlick5 as subsequently improved by Rigby and Wilson.6... 

On the other hand, the anodic oxidation of 1,3,5-cycloheptatrienes is one of the most powerful key tools for the preparation of a variety of non-benzenoid aromatic compounds such as tropylium salts, tropones, tropolones, 2H -cyclohcpta h furan-2-oncs and azulenes14. 

Nitrile oxides react with cycloheptatriene and its tricarbonyliron complex to give mixtures of adducts. In particular, for the complex, these adducts are 84, 85 (regioisomers at the uncomplexed double bond) and bisadduct 86. The regiose-lectivity of the reactions of cycloheptatriene is similar to that of the reactions of its tricarbonyliron derivative (246). 

Some features are characteristic of reactions of nitrile oxides with 2,4,6-cyclo-hep tatrien-l-imines (8-azaheptafulvenes). 1,3-Dipolar cycloaddition to the C=N double bond of N-aryl-2,4,6-cycloheptatrien-l-imines 142 (R = Ar), affording... 

The photo-oxidation of the aryl-substituted cycloheptatrienes 7-(/ -methoxy-phenyl)cycloheptatriene and 7-, 1- and 3-(/ -dimethylaminophenyl)cycloheptatrienes to the corresponding radical cations in de-aerated acetonitrile solution was accomplished by electron transfer to the electronically excited acceptors 9,10-dicyanoanthracene, iV-methylquinolinium perchlorate, iV-methylacridinium perchlorate and l,T-dimethyl-4,4-bipyridinium dichloride. In the case of l- p-methoxyphenyl)cycloheptatriene (62), deprotonation of the radical cation occurs successfully, compared with back electron transfer, to give a cycloheptatrienyl radical (63) which undergoes a self-reaction forming a bitropyl. If the photooxidation is done in air-saturated acetonitrile solution containing HBF4 and one of the acceptors, the tropylium cation is formed. Back electron transfer dominates in the / -dimethylaminocycloheptatrienes and the formation of the cycloheptatrienyl radical is prevented. 

Surprisingly, the partial reduction of quinone 137 is best achieved by refluxing in acetic or propionic acids (yield 67%). Thereby the acids suffer oxidative decarboxylation (82CL701 85BCJ515). Two further unexpected routes are based on the redox reaction with cycloheptatriene (85BCJ2072) and electrolysis under the conditions of the cyclic voltammetry measurements (87BCJ2497), respectively. 

Tropolone itself can be prepared in a number of ways, the most convenient of which involves oxidation of 1,3,5-cycloheptatriene with alkaline potassium permanganate. The yield is low but the product is isolated readily as the cupric salt ... 

Complexes of Cr, W, Mo, Fe, Ru, V, Mn and Rh form stable, isolable arene if -complexes. Among them, arene complexes of Cr(CO)3 have high synthetic uses. When benzene is refluxed with Cr(CO)6 in a mixture of dibutyl ether and THF, three coordinated CO molecules are displaced with six-7r-electrons of benzene to form the stable i/fi-benzene chromium tricarbonyl complex (170) which satisfies the 18-electron rule (6 from benzene + 6 from Cr(0) + 6 from 3 CO = 18). Complex formation is facilitated by electron-donating groups on benzene, and no complex of nitrobenzene is formed. Complex formation has a profound effect on reactivity of arenes, and the resulting complexes are used in synthetic reactions. The metal-free reaction products can be isolated easily after decomplexation by mild oxidation using low-valent Cr. Cycloheptatriene also forms a stable complex with Cr(CO)3 and its synthetic applications are discussed below. 

The oxidative decarboxylation of a cyclohepta[c c ]dithiophene (40), or the elimination of the trimethylammonium group in the salt (41) gave the fused cycloheptatriene (42) <82CS53>. However, in contrast to the isomeric system (43), a tropylium ion could not be formed from compound (42) <81JCS(P1)2904>. 

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