Paracyclophanes heterocyclic

SJ paracyclophane etc.] refers to the benzene rings in the structure, i.e. [8]-paracyclophane, [2,2,2]-para-cyclophane. Systems based upon heterocyclic molecules are also known. 

Carboxylate esters readily undergo photodecomposition with loss of carbon dioxide. Not surprisingly, lactones and related oxygen heterocycles undergo related transformations. A wide variety of lactones behave in this fashion443 for example, the cyclic dilactone (505) is converted on irradiation to the [2.2]paracyclophane (506).444 Of particular interest is the use of the /(-lactone (507) as a precursor of matrix-isolated cyclobutadiene (508).445... 

Apart from the role of cyclophanes as a model system for studying the electronic interaction between the aromatic moieties, chiral [2.2]paracyclophanes have also been utilized as planar chiral ligands in asymmetric catalysis. Recent advances and applications in this area have been reviewed [5, 6]. The synthesis of heterocyclic compounds based on [2.2]paracyclophane architecture, where the long-distance electronic communication and the planar chirality play significant roles in their application, has also been reported recently [7]. Although the preparation and application of chiral cyclophanes in asymmetric synthesis has attracted much attention for a long time, their chiroptical properties, especially the CD spectra, have rarely been paid attention or even completely ignored. 

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]. 

Very recently, Ma and coworkers prepared a planar-chiral Af-heterocyclic carbene silver complex based on [2.2]-paracyclophane (Scheme 3.18) [37]. The... 

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