Tropone complex

Furthermore, the homologous complex 286 condenses with ethyl orthoformate to give, in the course of a new y-tropolone synthesis, tropolone ether 287 by O-ethylation it is transformed to tropylium salt 288 (Scheme 72 70JA6382) the corresponding tropone complex was synthesized from dibenzotroporic and Cr (CO)6 [83AG(S)734]. 

The bicyclo[4.2.1]nonatriene 323 was prepared by the [6+2] cycloaddition of internal alkyne with the complex 322 under irradiation [79]. Ligand exchange of 323 with toluene liberated 324. The complex 325 underwent the [6+2] cycloaddition with two moles of terminal alkyne to give the tetracyclic compound 327 via 326. The [6+2] cycloaddition of the complex 322 and 1,7-octadiyne (328) afforded 329 as a primary product, which was converted further to 330 in 56% yield by further intramolecular [6+2] cycloaddition [80]. The tropone complex 331 underwent intramolecular [6+2] cycloaddition under irradiation to give the strained tricyclic compound 332 in moderate yield [81]. 

Tropones are another class of trienes that can be treated in this way. Both Michael additions and Diels-Alder reactions of the Ti" -tropone complex 10.21 occur exclusively at the uncomplexed alkene (Scheme 10.8). Addition in all cases was opposite the bulky Fe(CO)3 moiety. 

Tropones bind to diiron centres in a bis(allyl) fashion. Osella et al. have shown that the known tropone complexes, Fe2(GO)5 /x-(RG2R)3GO (R = Me, Et, Pr), undergo a reversible one-electron reduction on the cyclic voltammetry (GV) timescale however, electrogenerated anions rearrange smoothly to mononuclear tropone complexes over longer... 

It has long been known that reaction of Fe2(GO)9 with ethyne produced tropone as one of the products and using the dppm-stabilized complex, Fe2(CO)6(/ -GO)(/x-dppm) 11, this process has been shown to occur in a stepwise manner. Thus, the tropone complex 39 results upon prolonged photolysis of 11 and ethyne, while over shorter timescales dimetallacyclopentenone 37 and the flyover complex 38 are the major products (Scheme 4). " ... 

The freeze of equilibrium by the complexation method is also applicable to some other compounds. 2-Mercapto substituted tropone 32 has been reported to exist as an equilibrium mixture of 2-mercaptotropone (32 a) and 2-hydroxytropothione (32 b), and the latter is predominant both in solution 17) and in the solid state 18). The equilibrium is frozen and the former was isolated by inclusion complexation with 1. When a solution of 1 and 32 in petrol ether was kept, a 1 1 complex 33 composed of 1 and 32a was obtained in 90% yield as orange prisms of mp 101 to 103 °C19). The structure of 32a in 33 was elucidated by IR spectroscopy which showed vSH at 2482 cm-1 33 gave also absorptions of a strongly hydrogen-bonded hydroxyl group at 3270 cm 1. 

Rigby and coworkers305,309 also performed metal mediated [6 + 4] cycloadditions of heterocyclic trienes and tropones with various dienes. In concurrence with the all-carbon trienes, the electronic nature of the diene partners generally had little influence on the cycloaddition efficiency. The only reported exceptions are the reactions of thiepin-1,1-dioxides. Lower yields were observed in the reactions involving electron-deficient dienes in comparison with the reactions with electron-rich dienes. The reaction of complex 514... 

In the presence of aluminum chloride, tricyclic tropones 234a-c (Scheme 57) are easily reduced by complex hydrides to exceed the tropol stage and to afford tropilidenes 235a-c. Hydride abstraction (Section II,C,l,a) leads to tropylium salts 236a-c, but 236a could not be obtained in pure form [83CS(22)53]. 

Annulation of tricarbonyl cyclobutadiene iron to tropone and tropylium ion to give complexes 282 and 285 is achieved by Wittig cycloolefination of dialdehyde 281 with biphosphonium salts, 280 and 283, respectively (Scheme 71 77JA513 78AJC1607). 

Kato et al. (119) explored reactions of fulvenes with a variety of mesoionic heterocycles. Unfortunately, reactions of miinchnone 38 with several fulvenes afforded complex mixtures in each case, and no identifiable products were reported, although Friedrichsen and co-workers (120-122) previously reported the reaction between mtinchnones and fulvenes to give cycloadducts. Kato et al. (123) also studied the cycloaddition reactions of tropone with several mesoionic heterocycles. Despite heroic efforts, the reaction of tropone with miinchnone 38 was complex and could not be unraveled. However, as described later, the reaction of tropone with isomtlnchnones was successful. Wu et al. (124) effected the cycloaddition between a miinchnone and fullerene-60 (Ceo) to give the corresponding dihydropyrrole in excellent yield. 

Kato et al. observed that mesoionic 339 reacts with fulvenes, (119,151,152) benzocyclobutadiene (114), tropone (123), and triphenylphosphirene (112) to give cycloadducts 342-345, respectively. Only a sampling of products is given as these reactions are quite complex. For example, 2-ferf-butyl-6,6-dimethylfulvene gives a product type different from 342 (151,152). 

The 1,3-dipolar cycloaddition reactions of several other mesoionic heterocycles have been investigated since Potts review (1). Kato et al. (113,114,123) found that the l,3-thiazohum-5-olate (358) ring system affords low yields or complex reaction mixtures with benzocyclopropene (113), benzocyclobutadiene (114), and tropone (123). Likewise, Vedejs and Wilde (209) isolated in low yields a cycloadduct of 358d with thiopivaldehyde, along with a ring-opened thiamide. Also, 1,3-thiazo-lium-5-olate 359 reacts with thiopivaldehyde to give 360 (209). 

Access to alkyl substituted derivatives of the homotropylidene complexes is provided via the >j4-tropone iron complex by reaction with diazoalkanes, followed by mild thermolysis of the 3+2 py razoline adduct to give the corresponding homotropone complexes (equation 149)217,218. The 8,8-dimethyl derivative was used as starting material for the preparation of the fluxional ( 5-2,8,8-trimethylbicyclo[5.1.0]octa-2,4-dienylium)Fe(CO)3 cation complex219. More recently (homotropone)Fe(CO)3 was used for the synthesis of unique chiral 1,2-homoheptafulvene iron complexes220 221. 

Franck-Neumann has reported the synthesis of naturally occurring tropolones -thujaplicin and 3-do-labrin via the readily available [Fe(tropone)(CO)3] as shown in Scheme 23.43 A key step in the sequence is regiospecific acetylation of the [Fe(tropone)(CO)3] complex, a reaction which cannot be carried out on... 

The TCNE adducts of a variety of other [nq4-Fe(CO)3]- complexed trienes and tetraenes have been investigated. In most cases the adducts have been oxidatively cleaved from the metal with CeIV and the free ligands recovered in good yields. Reactivity patterns generally follow those described above for cy-cloheptatriene and cyclooctatetraene complexes. Specific complexes investigated include [Fe(2,4,6-cy-clooctatrieneone)(CO)3],61 [Fe(tropone)(CO)3],62,63 [Fe(heptafulvalene)(CO)3] and various 8-substituted... 

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