Facile Synthesis of Dibenzotetracenedione Derivatives by Rhodium‐Catalyzed [2+2+2] Cycloaddition/Spontaneous Aromatization

Abstract

It has been established that ac ationic rhodium(I)/ SEGPHOS complex catalyzes the [2+ +2+ +2] cycloaddition of biphenyl-linked 1,7-diynes with 1,4-naphthoquinone and anthracene-1,4-dione. Conveniently,s pontaneous aromatization proceeded upon removal of the rhodium complex by passing the reactionm ixture througha na lumina column, to give the corresponding dibenzotetracenediones and diben-zopentacenediones,r espectively,i ng ood yields. The obtained dibenzotetracenedione could be readily transformed into the corresponding dibenzotetracene in good yield. This dibenzotetracene showedb lue fluorescencew ith ag ood quantum yield, which was significantly higher than those of tetracene, tetrabenzotetracene, and hexabenzotetracene.Scheme1.Transition-metal-mediated [2+ +2+ +2] cycloaddition/aromatization of two alkynes with 1,4-naphthoquinone (2a); cod = 1,5-cyclooctadiene; Cp = cyclopentadienyl.

Recent Progress in Metal-Catalyzed [2+2+2] Cycloaddition Reactions

“…92 In 2019, Tanaka and co-workers succeeded in developing the Rh(I)/SEGPHOS [2+2+2] cycloaddition of biphenyllinked 1,7-diynes with 1,4-naphthoquinone and anthracene-1,4-dione (Scheme 31). 93 In the presence of 5-20 mol% the Rh complex, spontaneous aromatization occurred upon removal of the cationic Rh complex as well as the desired [2+2+2] cycloaddition to provide dibenzotetracenediones (11-86% yield) and dibenzopentacenediones (24-76% yield), respectively. In addition to unsymmetrical diynes,…”

Intramolecular rhodium-catalysed [2 + 2 + 2] cycloaddition of linear chiral N-bridged triynes: straightforward access to fused tetrahydroisoquinoline core

“…5 Among these transition-metal catalyzed transformations, [2 + 2 + 2] cycloadditions constitute an efficient and reliable method for accessing sophisticated ring structures, which can be useful intermediates in the synthesis of ubiquitous N-heterocyclic compounds. 6–12…”

“…Several types of cycloaddition processes can be achieved, including both intramolecular and intermolecular reactions. On the one hand, the partially intermolecular or semi-intramolecular version of these cycloadditions resulting in N-heterocyclic compounds, involve the use of nitrogen containing enynes, 6 diynes, 7 and alkenes/alkynes as partners or, alternatively, diynes and nitriles/heterocumulenes. 8 On the other hand, the intramolecular versions require nitrogen-tethered enediynes 9 or triynes.…”

Rh-Catalyzed [2 + 2 + 2] Cycloadditions with Benzoquinones: De Novo Access to Naphthoquinones for Lignan and Type II Polyketide Synthesis

“…Key potential problems that might undermine the eventual utility of the approach in Scheme C include (a) competing oligomerization of the diyne, (b) secondary cycloaddition via the quinone unit of the product, and (c) the reliability of the oxidation step. Recently reported cycloadditions between diynes and naphthoquinones to afford anthraquinones are conceptually related to the process proposed in Scheme C, but the conditions are not transferable to the synthesis of naphthoquinones . In this prior art, issue (b) was obviated and issue (c) was less problematic because the oxidation step is more facile .…”