Molecular Belts. 2. Substrate-Directed Syntheses of Belt-Type and Cage-Type Structures

The trebly-diastereoselective synthesis and structural characterization of two macropolycyclic derivatives, which are based upon building blocks incorporating six-membered rings that are both [a,c]- and [a,d]-fused, have been achieved by a Diels-Alder oligomerization reaction sequence. The angular syn bisdienophile 3 has been used as a Diels-Alder building block with the bisdiene 12 in a trebly-diastereoselective synthesis of the angular macropolycyclic derivative 5. The incorporation of two diametrically-opposed [a,c]-fused units into the skeleton of 5 imposes a conical nature upon the cavity compared with the structures of macropolycyclic compounds such as the cyclacene derivatives 1 and 2. The construction of the angular macropolycyclic derivative 5 anticipates the use of the C_3v trisdienophile 4, with the bisdiene 12, in the substrate-directed synthesis of a novel cage-like compound dubbed trinacrene 6. The structural characterization of both the angular macropolycyclic derivative 5 and trinacrene 6 has been achieved by high-field NMR spectroscopy and FABMS. In each case, the operation of treble diastereoselectivity during each cycloaddition step dictates the structures of the products, underlining the utility of these stereoregular Diels-Alder oligomerizations to control the formations of molecular structures.