Phenanthrene 1 -2-aryl-1 -alkene

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. 

The palladium-catalyzed reaction of allyl chloride 11 with the benzyne precursor 104 to produces phenanthrene derivatives 131 is also known [83]. A plausible mechanism for this intermolecular benzyne-benzyne-alkene insertion reaction is shown in Scheme 38. Initially n-allyl palladium chloride la is formed from Pd(0) and 11. Benzyne 106, which is generated from the reaction of CsF and 104, inserted into la to afford the aryl palladium intermediate 132. A second benzyne insertion into 132 produce 133 and subsequent carbopalladation to the alkene afford the cyclized intermediate 134. f>- Iydride elimination from 134 followed by isomerization gave 9-methylphenanthrene 131. 

In this field, Cheng et al. have also developed the carbocyclization reaction of aromatic iodides, bicyclic alkenes, and arynes to afford various armulated 9,10-dihydrophenanthrene derivatives 117 (Scheme 12.58) [102]. A related eross-coupling of arynes with aryl iodides but using alkynes as the third component has been described by Larock and Liu, furnishing substituted phenanthrenes 118 (Scheme 12.58) [103]. 

SCHEME 3.18 Palladium-catalyzed carbocyclization of aryl iodides, bicyclic alkenes, and arynes. Synthesis of annulated 9,10-dihydro-phenanthrenes. 

Several name reactions are promoted by AICI3. For example, the Darzens-Nenitzescu reaction is simply the acylation of alkenes. The Ferrario reaction generates phenoxathiins from diphenyl ethers (eq 19) The rearrangement of acyloxy aromatic systems is known as the Fries rearrangement (eq 20). Aryl aldehydes are produced by the Gatterman aldehyde synthesis (eq 21). The initial step of the Haworth phenanthrene synthesis makes use of a Friedel-Crafts acylation. The acylation of phenolic cort tounds is called the Houben-Hoesch reaction (eq 22). The Leuckart amide s)oithesis generates aryl amides from isocyanates (eq 23). ... 

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