Heteroarene-fused barrelenes,

Heteroarene-fused barrelenes are generally synthesized from a-diketones 7 and 1,2-diamines. Pyrazinobarrelenes"" could be prepared either by condensation of a-diketones 7 with ethylenediamine followed by oxidative generation of the pyrazine ring or by direct condensation of 7 with diaminomale-onitrile (Scheme 2). Quinoxalinobarrelenes, " benzo(g]quinoxalinobarrelenes, " and dibenzo(//ij-quinoxalinobarrelenes are easily obtained by simple condensation of 7 with o-phenylenediamines, 2,3-diaminonaphthalene, and 9,10-diaminophenanthrene, respectively. 

Within the barrelene system, the photochemistry of dibenzobarrelene and its derivatives have been extensively investigated, presumably due to their easy accessibihty as well as the interesting mechanistic aspects. This material is covered in depth in other articles - and discussed here to the extent required for comparison with photochemical studies of heteroarene-fused barrelenes. Ciganek reported that the acetone-sensitized reaction of dibenzobarrelene 32 results in the formation of dibenzosemibuUvalene 34. 

As a further extension of the photochemistry of heteroarene-fused barrelenes, dibenzo(/,/i]-quinoxali-nobarrelenes have been subjected to photoisomerization in this laboratory. Upon direct irradiation of 101 in cyclohexane, the DPM product 102 and the ADPM products 103 and 104 are obtained. The vinyl-vinyl bridged product 102 is minor (Scheme 12). Similarly, the reaction of heterobarrelene 105 under direct irradiation proceeds through both the DPM and the ADPM modes and produces SBs 106-108. Again, the DPM product 106 is formed as a minor photoproduct (Scheme 13). ... 

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