English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Zendy Plus

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Zendy Tools

Zendy Open

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(enoltriÑuoromethanesulfonate) 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 ¡C via a SaitoÈMyers 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 SaitoÈMyers 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 (SaitoÈMyers: 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 SaitoÈMyerscyclization product 55 is calculated to be considerably more stable (35.3 kcal mol~1) than theneocarzinostatin-type cycloaromatization product 56

new journal of chemistry

Straightforward syntheses of biradical-producing bicyclic dienediynes—dienediyne ketones cycloaromatize ia the Saito–Myers and not ia the neocarzinostatin pathway