In Pursuit ofcis,cis,cis‐Cyclonona‐2,5,8‐triene‐1,4,7‐trione – An Adventure in Medium‐Sized Ring Chemistry

Abstract

Attempts to synthesize the long soughtafter tris‐π‐homobenzene cis,cis,cis‐2,5,8‐cyclononatriene‐1,4,7‐trione, via the newly prepared cyclononane‐1,4,7‐trione (C9H6O3), through base‐catalysed threefold HBr elimination from an efficiently prepared and stereochemically uniform tribromo derivative, failed due to typical medium‐ring complications, transannular reactions and an exceptional ease of polymerization. In the cations generated in the vapour phase through electron‐impact ionization (MS), the threefold elimination of (H)Br, competing with the elimination of CO, led to C9H7O3+ ions, whereas the impressively neat anionic three‐step fragmentation pathway resulted in C9H6O3– ion(s). Whilst the compositions of these bromine‐free ions, which were in part computationally approached {B3LYP/6‐31+G(d,p)}, and their assignments appeared compatible with the protonated and anionic target molecules, their true natures remain open. X‐ray structural analyses for several (bridged) nine‐membered ring compounds are provided. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Oxatriquinane and Oxatriquinacene: Extraordinary Oxonium Ions

“…The hydrolysis product 14 was oxidized to the ketone 15 (Scheme ), which could be brominated in the positions α to the carbonyl group in modest but workable yield by simple reaction with Br 2 . Elimination to 17 followed by Luche reduction gave dienol 18 , which closed down to the oxatriquinacene cation 2 on treatment with triflic acid.…”

Syntheses of Cyclotriveratrylene Analogues and Their Long Elusive Triketone Congeners

“… 14 In fact, no report of successfully accessing the triketone of cyclotriveratrylene or any related analogue has ever been issued, with some authors suggesting that such an outcome is unachieveable. 12 , 13 , 15 Herein, we disclose a unique route to synthesize a novel cyclotriveratrylene-like analogue, one that may prove extendable to other synthetically challenging congeners, and a procedure that successfully oxidized that material to a triketone. In addition, we show that a second cyclotriveratrylene-like substrate is capable of forming a similar triketone, establishing in the process what we believe are the structural guidelines for when triketones can be formed with electron-rich substrates in preference to the spirocycles observed in past studies.…”

Extreme Oxatriquinanes: Structural Characterization of α-Oxyoxonium Species with Extraordinarily Long Carbon–Oxygen Bonds

“…Finally, analogous attempts were made to produce 15 and 16 from literature compounds 23 and 24 , which are prepared from 1,4,7-cyclononatrione 22 (Scheme ) . It can be envisaged that, like 17 and 20 , diol 23 could simply be protonated to give 15 .…”