@Article{publ_mods_00000056, author = {Ferri, Fabiola and Br{\"u}ckner, Reinhard and Herges, Rainer}, title = {Straightforward syntheses of biradical-producing bicyclic dienediynes---dienediyne ketones cycloaromatize ia the Saito--Myers and not ia the neocarzinostatin pathway}, journal = {New Journal of Chemistry}, year = {1998}, publisher = {Royal Society of Chemistry}, address = {London}, volume = {22}, number = {5}, pages = {531--545}, keywords = {Neocarzinostatin}, abstract = {The dienediyne models 23 and 28 of the pharmacophore of the antitumor natural product neocarzinostatin were prepared. Each synthesis requires only six steps from a-formylcyclohexanone. Our approach uses two key steps. The Ðrst consists of one-pot biscoupling reactions between propargyl alcohol, 2,2-dimethyl-3-butyn-1-ol and the bis(enoltri{\~{N}}uoromethanesulfonate) 17. The second key step corresponds to ring-closing pinacol coupling reactions of the dialdehydes 20 and 25. The dienediyne models 23 and 28 cycloaromatized efficiently when treated with methyl thioglycolate and 1,4-cyclohexadiene at 25 {\textexclamdown}C via a Saito{\`E}Myers cyclization4 (to give the octahydroanthracenones 29, iso-29 and octahydrophenanthrenones 34, 35, respectively); in addition, we isolated compounds tentatively assigned as the octahydrobenzazulenones 30 and iso-30, which would stem from a competing Schmittel cyclization. According to density functional theory (B3LYP/6-31G*) and ab initio calculations [CASMP2(2.2)/6-31G//CAS(2.2)/6-31G], the core structures of the octahydroanthracenones and octahydrophenanthrenones obtained here and elsewhere form via the Saito{\`E}Myers cyclization of enyneallenyl ketones 53 to toluene-a,meta biradicals 55 and not via neocarzinostatin-like cycloaromatizations of the tautomeric enyne[3]cumulenols 54 to styrene a,meta-biradicals 56. This is so because, on the one hand, the two cyclization modes are predicted to have similar activation barriers (Saito{\`E}Myers: 16.0 kcal mol{\~}1; neocarzinostatin type: 18.3 kcal mol{\~}1) but, on the other hand, the enyneallenyl ketone 53 is a much more stable (21.1 kcal mol{\~}1) cycloaromatization substrate than the enynecumulenol 54. In addition, the Saito{\`E}Myers cyclization product 55 is calculated to be considerably more stable (35.3 kcal mol{\~}1) than the neocarzinostatin-type cycloaromatization product 56.}, note = {http://xlink.rsc.org/?DOI=a709205i}, issn = {1144-0546}, doi = {10.1039/a709205i}, url = {https://macau.uni-kiel.de/receive/publ_mods_00000056}, url = {https://doi.org/10.1039/a709205i}, file = {:https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/macau_derivate_00000016/a709205i.pdf:PDF}, language = {en} }