| We investigate cycloaromatization reactions of C10H4 enediyne isomers and their derivatives. These reactions are of interest in the fields of organic chemistry, combustion chemistry, and astrochemistry.;Using NMR and GC-MS, we show that heating a solution of tetraethynylethene in the presence of a trapping agent affords naphthalene via a double Bergman cyclization process; this is the first demonstration of a tetrayne undergoing a Bergman cyclization. When no trapping agent is present, tetraethynylethene isomerizes through a Bergman rearrangement upon heating.;We demonstrate that heating a solution of unsymmetrical tetrayne in the presence of 1,4--cyclohexadiene trapping agent facilitates cycloaromatization to 1,4-diethynylbenzene. Because the Bergman rearrangement of the unsymmetrical tetrayne is a degenerate rearrangement, a deuterio-labeled analogue was synthesized to enable further investigation of this reaction.;In a computational study of the aforementioned cycloaromatization reactions, we describe optimized structures of four C10H4 tetraynes, 1,2-diethynylbenzene, and cis-hex-3-ene-1,5-diyne and calculate potential energy surfaces for related cycloaromatization pathways using density functional theory methods. Based on general good agreement of our calculations with literature precedents, B3LYP/6-3 1G* appears sufficient for developing relative trends in structural properties and cyclization parameters for our systems. All of the diradical intermediates in the corresponding Bergman cyclization reactions are predicted to have singlet ground states. Trends in calculated c-d distance and predicted cyclization barriers generally agree with preliminary experimental results of cycloaromatization studies in our laboratory.;We synthesize a symmetrical tetrabromotetrayne in one step from a tetrakis(trimethylsilyl) precursor. Heating a solution of the symmetrical tetrabromotetrayne at 170°C in the presence of 1,4-cyclohexadiene trapping agent enables a double cycloaromatization to yield 2,3,6,7--tetrabromonaphthalene. The tetrabromo-substituted tetraynes and the corresponding trapping products are potential building blocks for highly-conjugated networks. We have also synthesized three tetraphenyl and one tetrakis(trimethylsilyl)-substituted tetrayne and four corresponding trapping products. Because of these synthetic efforts, we are poised to expand and define the scope of cycloaromatization reactivity of a series of tetraethynylethene derivatives. |
