Syntheses of Novel Belt-Type Molecules Using Dewar Benzenes.

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We have successfully synthesized and characterized novel p-phenylene-based strained macrocycles by introducing 1,4-acetal-bridged Dewar benzene as a building block. The present results demonstrate that a Dewar benzene unit can be exploited as a masked p-phenylene unit for the constraction of strained macrocyclic systems. By using other spacers and/or connection modes, a variety of p-phenylene-containing strained macrocycles with unique structures and properties may well become available based on the present building block aproach.We have also successfully developed a new bisdiene molecule that produces a Dewar benzene skeleton upon two successive Diels-Alder reactions with activated dienophiles. Dehydrogenation of the 1: 2 adducts provides the corresponding Dewar form of polyacenes. Similar bisdiene systems possessing other 1,4-bridging units may also be available based on the synthetic scheme. Therefore, the present results open a unique and versatile route to Dewar derivatives which, in turn, would be regarded as potential precursors for novel cyclophanes as well as belt-type molecules.