Abstract
[2 + 2 + 2] cycloaddition of a 1,2-bis(propiolyl)benzene derivative with terminal and internal alkynes takes place in the presence of [Ir(cod)Cl]2 (cod = 1,5-cyclooctadiene) combined with bis(diphenylphosphino)ethane (DPPE) to give anthraquinones in 42% to 93% yields with a simple experimental procedure. A fluorenone derivative can also be synthesized by iridium-catalyzed [2 + 2 + 2] cycloaddition of a benzene-linked ketodiyne with an internal alkyne to give a 94% yield.
Highlights
Anthraquinones and their derivatives are important structures found in natural products and bioactive compounds and show a broad range of bioactivities including anti-tumor [1,2], cytotoxic [3], anti-cancer [4,5,6], anti-bacterial [7,8], laxative [9], anti-arthritic [10], anti-fungal [11], anti-platelet [12,13], and neuroprotective effects [14]
The development of synthetic methods for the formation of multi-substituted anthraquinones is an important research topic, and several synthtic methods including the oxidation of anthracene [21,22], the Friedel-Crafts reaction of phthalic anhydride [23], and the Diels-Alder reaction of naphthoquinones followed by aromatization [24] have been developed
The phosphine ligand was found to improve the yield of anthraquinone 3a
Summary
Anthraquinones and their derivatives are important structures found in natural products and bioactive compounds and show a broad range of bioactivities including anti-tumor [1,2], cytotoxic [3], anti-cancer [4,5,6], anti-bacterial [7,8], laxative [9], anti-arthritic [10], anti-fungal [11], anti-platelet [12,13], and neuroprotective effects [14]. The development of synthetic methods for the formation of multi-substituted anthraquinones is an important research topic, and several synthtic methods including the oxidation of anthracene [21,22], the Friedel-Crafts reaction of phthalic anhydride [23], and the Diels-Alder reaction of naphthoquinones followed by aromatization [24] have been developed. After the success of stoichiometric reactions with a large amount of highly toxic Ni(CO)4 [31] and isolated naphthoquinone-fused rhodacyclopentadiene [32], catalytic reactions were realized by the use of Ni(PPh3 ) (CO)2 [33], CpCo(CO)2 [34], and RhCl(PPh3 )3 [35]
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