Synthesis of multiply bridged acetylenic thiacyclophanes
Description
Interest in high carbon containing spheroidal molecules led to the syntheses of two thiacyclophanes, 7,19,28-trithiatetracyclo (11.11.7$\sp{3,23}.11\sp{11,15}$) tritriaconta-1,3(32),11(33), 12,14,23-hexaene-4,9,16,21,25,30-hexayne and 5,14,23,32,41,50-hexathiaheptacyclo (0$\rm\sp{1,18}.0\sp{9,46}.0\sp{10,27}.0\sp{19,36}.0\sp{28,45}.0\sp{ 37,54}\rbrack tetrapentacosa-11(54),9,18,27,36,45-hexaene-2,7,11,16,20,24,29,33,38,43,47,52-dodecayne.$ These cage structures are potential precursors to hydrocarbon spheres consisting of two identical halves connected by out of plane ethylene bridges. The extended conjugation these molecules possess, in addition to these out of plane unsaturated bridges, could result in interesting photochemical and electronic properties Various problems encountered involving solubility, polymerization, and stability of the intermediates led to changing approaches for the preparation of the above compounds. The thiacyclophanes have been prepared using functional group transformations spanning several steps. The key processes in these syntheses are the palladium and copper mediated coupling of acetylenes and aryl halides, formation of the desired heteroatom bridges, and the homologation of carbonyl moieties to obtain propargyl systems. The role of copper acetylides in the cross coupling reaction with aryl halides, mechanism of the coupling reaction, and attempted synthetic routes are discussed in detail. Previously reported thiacyclophanes do not contain acetylenic substituents on the aromatic cores. Due to the propargylic groups on these molecules, the sensitivity of such systems to strongly acidic or basic conditions, electrophilicity, and thermal instability are greatly increased in comparison to similar compounds prepared previously. In order to avoid complete decomposition of the material, the multi-step schemes pursued involved extremely mild conditions after the incorporation of the propargyl substituents