Intramolecular addition reactions phenanthrenes

Irradiation of phenanthrene in the presence of the electron deficient styrene (376) and hexamethyldlsilane is reported to yield (377) by a mechanism involving electron transfer to the styrene. The reglochemlstry of the light Induced intramolecular addition of eunines to excited styrenes in (378) has been examined.This reaction also proceeds by electron transfer from the amine to the excited styrene chromophore. 

In this section we must also mention the syntheses of cyclopentano-phenanthrene derivatives described in Scheme 88. These include, in the first place, attempts to apply the Robinson synthesis (Chapter II, Schemes 24 and 25) to the preparation of tetracyclic products with an angular methyl group at CiQ. By this method, for example, from the acetylmethylcyclo-hexene (63) and 1,5-decalindione (4) it was expected to obtain the diketone (65) through a sequence of Michael addition reactions and intramolecular crotonic condensation. However, it was found that the presence of the ce-methyl group in the acetylcyclene (63) suppressed the Michael reaction and... 

The analogous primary amine had been earlier studied by Wubbels and gave only the photo-Smiles reaction, but this process was not observed for the present system and the reaction is suggested to proceed by a photo-electron transfer mechanism to yield the radical ion pair. Photoaddition of N-H bonds to aromatic compounds has been known for some years, and the intramolecular process which leads to cyclization products has been reported for the reaction of 9-(aj-anilinolalkyl)phenanthrenes (220). The formation of the spiro-compounds (221) by addition of the N-H bond across the phenan-threne 9,10-positions is suggested to arise from the intramolecular exciplex in... 

In contrast to the preferred meta mode of intramolecular photoaddition of 5-phenyl-l-pentenes, where the alkene and benzene groups are separated by three atoms, irradiation of the styrene (64) yields a single stereoisomer of the ortho adduct (65). In (64), not only are the reacting units separated by 4 atoms, but also it is the styrene rather than the benzene which is excited. Comparable photoreactivity is seen for phenanthrene-styrene systems such as (66) which yield 2+2 adducts (67) along with products derived from competing Paterno-Btichi reaction of the ester carbonyl with the alkene side chain. The photochemical cycloaddition also proceeds in an intermolecular fashion between the ester of 9-phenanthrene carboxylic acid and para-methoxy-0-methylstyrene. The mechanism of this reaction is shown to involve addition of the styrene to the singlet excited state of the phenanthrene derivative. °... 

In all cases presented above, annulation reactions were limited to intramolecular arrangements. There are also transformations involving two independent reaction partners. In 2005 a Cr-mediated synthesis of PAHs from halobiaryls was published [94]. The 2,2 -dihalobiaryl starting material 150 is first treated with BuLi before addition of the Cr reagent. Final treatment with an acetylenic reaction partner delivers the phenanthrene core 151 (Scheme 38). Recently, Wu and coworkers presented a Pd-catalyzed version starting from 2,2 -diiodobiphenyls to access substituted phenanthrenes [95]. 

Intramolecular photochemical cyclization of N-substituted-3-alIyloxy-5,5-di-methylcyclohexenones (312) gives 2-aza- or 2-oxa-bicyclo[2,l,l]hexane derivatives (313). The reaction is sensitized by benzophenone and quenched by piperylene or phenanthrene. The products of parallel addition (bicyclo[2,2,0]hexane derivatives) are not found. 

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