Polycyclic aromatics => aryl alkenes

A number of l-aryl-2-thienylethylenes have been photocyclized in the presence of an oxidizing agent (usually iodine) to polycyclic aromatic compounds. Representative examples are given in Table 1. The mechanism, as with the conversion of stilbene to phenanthrene, probably involves conversion of the trans-alkene to the c/s-form, cyclization to the dihydro isomer, and oxidation of the latter to the fully aromatic compound. The yield of the cyclized product seems to decrease when the ethylene is attached to the /3-position of the thiophene. 

Reduction of organic substrates to dianions can be divided into (a) reductions of polycyclic aromatics, (b) reductions of aryl-substituted alkenes or alkynes, (c) reductions of 4n 7i-electron systems, and (d) reduction of aryl ketones and derivatives. 

The reduction of an aryl-substituted alkene or alkyne by Li metal to give a dilithium dianion is similar to the reduction of a polycyclic aromatic compound. The products are represented by localized structures in which a C—C bond is reduced, e.g., in stilbene ... 

Various diaryIcarbenes, whose aryl groups belong to a polycyclic, aromatic system, react with a number of alkenes and form spirocyclopropanearenes. Such carbenes are generally prepared by thermal and photochemical decomposition of the corresponding diazo compounds. Other... 

Treatment of aryl azides with AICI3 has been reported to give polycyclic aromatic compounds (eq 7), or aziridines when the reactions are run in the presence of alkenes (eq 8). ... 

If the allyl group of the aryl allyl ether featured a tri- or tetra-substituted alkene, then the thermodynamic isomerization to the aromatic benzofuran could not occur, and dihydroben-zofurans were consequently produced in good to excellent yields (Figure 9.8). As in the benzofuran systems, a host of aryl and alkyl substitution patterns were tolerated in this oxidative cyclization. A number of polycyclic and highly functionalized dihydrobenzofurans were obtained via this palladium(II)-catalysed oxidation. 

The acid-catalysed rearrangement of N-aryl 2-azabicyclo [3.1.0]hexanes, where the aromatic system is conjugated with an alkene group located at the ortho position relative to the nitrogen atom, gives dihydroquinolines or polycyclic aminocyclobutanes via an iminium intermediate formed by protonation of the aminocyclopropane moiety... 

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