Thiophene - cyclopentadienone

The preparation of thiophene-cyclopentadienone cooligomers 104 is accomplish by treating the bisalkyne 103 with 2,6-xyIyl isocyanide (XyNC) in the presence of Ni(cod)2 (Eq. 19) <94CC229>. 

Thiophene-cyclopentadienone cooligomers have been similarly prepared from an acetylenic precursor (Scheme 143) <94CC229>. The crucial step is the intramolecular cyclization of a diyne with 2,6-xylylisocyanide. 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

Metallacyclopentadienes undergo a range of synthetically versatile reactions which proceed with extrusion of the metal atom and attendant ligands. Thus, reactions with alkenes and alkynes afford cyclohexa-1,3-dienes and arenes (Scheme 6), and thiophenes, selena-cyclopentadienes, pyrroles and cyclopentadienones (indenones, fluorenones) can be obtained by treatment with sulfur, selenium, nitroso compounds and CO, respectively. The best studied substrates for such reactions are cobaltacyclopentadienes of the type (24a), which have been converted into a wide variety of arenes, cyclohexadienes and five-membered heterocycles, many of which would be very difficult to obtain by conventional organic procedures (74TL4549, 77JOM(139)169, 80JCS(P2)1344). 

This has been essentially accomplished in a case of the diene-dienophile monomer polymerization (6, 7, 8, 16). This excellent work makes use of the reaction of such dienes as cyclopentadienones, a-pyrones, and thiophene dioxides with dienophiles. The resulting adduct, a protected or inactive diene, loses carbon monoxide, carbon dioxide, or sulfur dioxide at elevated temperatures to form a diene. Thus when a Ws-malei-mide reacts with one mole of a cyclopentadienone, the resulting adduct will lose carbon monoxide at 150—260° in an inert solvent to form an active intermediate diene-dienophilic monomer which readily poly-... 

A novel extrusion of S02 is reported for the dithiine dioxides 104 to afford low yields of the thiophenes 105 and 106. The exact step at which the S02 loss occurs is not known but the proposed intermediates 107 and/or 108 have support from the formation of pyrrole derivatives when the reaction is carried out in the presence of n-butylamine103. Sunlight-induced extrusion of sulphur dioxide from the pyranone dioxide 109 is similar to the above and results in the formation of the reactive cyclopentadienone 110 which can be trapped by dienophiles or in their absence forms a trimer104. The platinum complex 111 is photochemically labile and decomposes into benzyne on irradiation105. 

Various polymerization route with unique starting monomer [64] have been developed, e.g., topochemical poly(diacetylene) synthesis with pyrrole-, thiophene-, -Si-groups dienophilic addition of maleic imides, Diels-Alder polymers via cyclopentadienone derivatives. 

Many thiophens are surprisingly reactive towards dicyanoacetylene in the Diels-Alder reaction. Since the adducts irreversibly lose sulphur and the starting thiophens are usually readily available (in contrast to the corresponding butadienes or cyclopentadienones), this constitutes a useful route to... 

Rh(PPh3)3Cl to diyne (115). A similar reaction occurs with the diene (116). Conversion of these rhodium species into cyclopentadienones (with carbon monoxide) or into substituted furans, thiophens, or selenophens (with oxygen, sulphur, or selenium, respectively) can be effected. ... 

More recently, AE values of 1.20-1.30 eV were reported for compounds 96 combining thiophene and cyclopentadienone rings [178]. 

The polymerization of bis(dienophiles) with cyclopentadienones, a-pyrones, and thiophene dioxides has yielded some very high molecular weight... 

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