Cyclophanes 2 cyclophane, multibridged

Thermolysis of (34) gives (33). Pyrolyses of o-(chloromethyl)toluenes give o-xylylenes, which thermally dimerize to [2]cyclophanes (80ACR65). This technique has been successfully applied to the preparation of multibridged pyridinophanes (8lAG(E)57l). 

Irradiation of ort/zo-diarylarenes (e.g. o-terphenyls) results exclusively in condensed PAH as products from photocyclization reactions (e. g. triphenyl-enes, see [84]) and, of course, no [2+ 2]cycloaddition is observed. This fact enables the use of higher concentrations of ortho-diarylarenes compared to stilbenes in a photocyclization reaction as outlined in Scheme 16 for the synthesis of benzo[c]naphtho[2,1 -p]chrysene (15b) from 1,3,5-tristyrylbenzene (38, c <0.2 mmol 1 1 [85]) or 1,2 l, 2"-ternaphthalene (39, c = 20 mmol 1 1 [84 c]) respectively. If higher concentrations of 38 were applied, [2 + 2] cycloaddition reactions yielding multibridged cyclophanes were observed almost exclusively [85]. 

More than 90 years after the first reported synthesis of [2.2]metacyclophane [1] and nearly 50 years after the synthesis of [2.2]paracyclophane, [2] cyclophane chemistry is still a field of ongoing research. In the beginning, work had been focused on the development of new synthetic methods yielding cyclophanes and ansa-compounds and the investigation of their physical properties. Later, the scope was extended to the incorporation of heterocycles into phanes and the more sophisticated techniques allowed the synthesis of multibridged and multilayered phanes. All this has been extensively reviewed [3]. 

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