Polycyclic aromatic hydrocarbons regioselectivity

Pressure influences the regioselectivity and the endo-exo diastereoselectivity of the cycloadditions. All the cycloadducts were converted into polycyclic aromatic hydrocarbons by treatment over a Pd/charcoal catalyst. This approach provides a new and efficient route to a broad variety of polycyclic aromatic hydrocarbons [36]. 

A new cascade reaction of aromatic aldehydes with terminal conjugated alkynes produces a range of polycyclic aromatic hydrocarbons.195 The effect of temperature on regioselectivity is discussed. 

Scheme IS dq>icts a high yield, general method for specific ortho allgriation of polycyclic aromatic hydrocarbons. In this example, biphenyl is subjected to reductive methyladon followed by oxidative rearrangement with trityl tetrafiuoioborate to give 2-methylbipbenyl. In unsymmetrical substrates the regioselectivity is poor, phenanthiene gives a 3 2 mixture of 4-methyl- and 1-mediyI-phenanlhrene.

A considerable degree of control of the regioselective hydrogenation of polycyclic aromatic hydrocarbons has been achieved through the choice of catalyst and optimized conditions. The review by Nishimu-ra and Takagi and Rylander s monographs furnish many examples and references. - ... 

The reaction of polycyclic aromatic hydrocarbons with [hydroxy(tosyloxy)iodo]benzene in the presence of trimethylsilyl isothiocyanate leads to the regioselective thiocyanation of an arene nucleus, as illustrated by the reaction of anthracene shown in Scheme 3.213 [274],... 

Resonance structures aid in predicting the regioselectivity of larger polycyclic aromatic hydrocarbons... 

In Summary Naphthalene is activated with respect to electrophilic aromatic substitution favored attack takes place at Cl. Electrophilic attack on a substituted naphthalene takes place on an activated ring and away from a deactivated ring, with regioselectivity in accordance with the general rules developed for electrophilic aromatic substitution of benzene derivatives. Similar considerations apply to the higher polycyclic aromatic hydrocarbons. 

Among polycyclic hydrocarbons, there is a considerable interest in poorly studied compounds having a benzopentalene skeleton. The presence of a fused aromatic ring is expected to restrict possible rearrangements, therefore ensuring relatively high regioselectivity. 

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