Copper(0)/Selectfluor System-Promoted Oxidative Carbon-Carbon Bond Cleavage/Annulation of o-Aryl Chalcones: An Unexpected Synthesis of 9,10-Phenanthraquinone Derivatives

Article abstract of DOI:10.1021/acs.joc.6b02212

A general and efficient protocol for the synthesis of 9,10-phenanthraquinone derivatives has been successfully developed involving a copper(0)/Selectfluor system-promoted oxidative carbon-carbon bond cleavage/annulation of o-aryl chalcones. A variety of substituted 9,10-phenanthraquinones were synthesized in moderate to good yields under mild reaction conditions.

Full text of DOI:10.1021/acs.joc.6b02212

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Article
Copper(0)/Selectfluor System-promoted Oxidative Carbon-
Carbon Bond Cleavage/Annulation of o-Aryl Chalcones: An
Unexpected Synthesis of 9,10-Phenanthraquinone Derivatives
Hanyang Bao, Zheng Xu, Degui Wu, Haifeng Zhang, Hongwei Jin, and Yunkui Liu
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.6b02212 • Publication Date (Web): 02 Dec 2016
Downloaded from http://pubs.acs.org on December 2, 2016
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The Journal of Organic Chemistry
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Copper(0)/Selectfluor System-promoted Oxidative Carbon-Carbon Bond
Cleavage/Annulation of o-Aryl Chalcones: An Unexpected Synthesis of
9,10-Phenanthraquinone Derivatives
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Hanyang Bao, Zheng Xu, Degui Wu, Haifeng Zhang, Hongwei Jin* and Yunkui Liu*
State Key Laboratory Breeding Base of Green ChemistryꢀSynthesis Technology, Zhejiang University
of Technology, Hangzhou 310014, People’s Republic of China
Eꢀmail: ykuiliu@zjut.edu.cn; jhwei828@zjut.edu.cn
TOC graphic
O
O
Cu(0) (10 mol %)
O18
CHO18
Selectfluor (2 equiv)
MeCN/H2O18 = 50:1 (V/V)
R1
R3
R1
R3
R2
25 °C, 12-24 h
R2
Mild reaction conditions;
Inexpensive copper catalyst;
Easy availability of starting materials.
ABSTRACT
A general and efficient protocol for the synthesis of 9,10ꢀphenanthraquinone derivatives has been
successfully developed involving a copper(0)/Selectfluor systemꢀpromoted oxidative carbonꢀcarbon
bond cleavage/annulation of oꢀaryl chalcones. A variety of substituted 9,10ꢀphenanthraquinones were
1
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The Journal of Organic Chemistry
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synthesized in moderate to good yields under mild reaction conditions.
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Introduction
9,10ꢀPhenanthraquinone scaffold is often seen in some natural, metabolic, or synthetic products
which display unique biological activities.1 Besides, 9,10ꢀphenanthraquinones can serve as useful
intermediates for the preparation of many biologically interesting compounds2 as well as functional
molecules in materials science.3 Thus, the development of efficient methods for the preparation of
9,10ꢀphenanthraquinones is highly desirable. Traditionally, 9,10ꢀphenanthraquinones are
synthesized through oxidation of phenanthrenes with a variety of oxidants.4,5 Alternative methods
include
oxidation
of
several
phenanthreneꢀoriginated
substrates
such
as
9,10ꢀdihydrophenanthrenes,6 10ꢀhydroxyphenanthrenꢀ9(10H)ꢀones,7 9ꢀphenanthrenols,8 and
phenanthreneꢀ9,10ꢀdiol.9 However, most of these oxidative reactions suffer from one or more
limitations such as the use of expensive catalysts, the employment of toxic oxidants, and lack of
generality. In addition, the construction of the 9,10ꢀphenanthraquinone scaffold from
nonꢀphenanthreneꢀbased
precursors,
e.g.
2ꢀacetylbiphenyls,10
dimethyl
biphenylꢀ2,2'ꢀdicarboxylate,11 benzils,12 benzoins,13 biaryloxalic acids,14 or 2,2'ꢀdilithiobiphenyl,15
has also been reported. Despite their merits, most of these methods have several drawbacks such as
narrow scope of substrates, multistep processes, and low yields. Overall, up to now, general and
efficient methods enabling the synthesis of different substituted 9,10ꢀphenanthraquinones remain
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very limited.12d,e,14 Herein we describe a general and efficient method to access a range of
substituted 9,10ꢀphenanthraquinones through a copper(0)/Selectfluor systemꢀpromoted oxidative
carbonꢀcarbon bond cleavage/annulation of oꢀaryl chalcones under mild reaction conditions
(Scheme 1).16
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As part of our ongoing effort to develop mild and efficient catalyst systems for the construction
of useful molecules,17 we have recently disclosed that the combination of copper powder and
Selectfluor (1ꢀ(chloromethyl)ꢀ4ꢀfluoroꢀ1,4ꢀdiazoniabicyclo[2.2.2]octane bis(tetrafluoroborate),
FꢀTEDAꢀBF4) may generate an active XCuOH species (X = F or BF4) which is easily able to
undergo oxycupration toward carbonꢀcarbon multiple bonds and induce successive tandem
reactions.18 For example, we have successfully achieved oxidative annulation of 1,5ꢀ and
1,6ꢀenynes by the Cu(0)/Selectfluor system to access 3ꢀformylꢀ1ꢀindenones18b and fluorinated
fluorenones,18c respectively. Inspired by these findings, we envisioned that the oxycupration of the
CꢀC double bond in oꢀaryl chalcone 1 by the Cu(0)/Selectfluor system followed by a
dehydrogenative crossꢀcoupling and an oxidation of the hydroxy group would result in the formtion
of annulated products 4. To our surprise, the desired products 4 were not obtained whereas
9,10ꢀphenanthraquinones 2 were unexpectedly formed in moderate to good yields (Scheme 1).
Scheme 1. Unexpected Synthesis of 9,10-Phenanthraquinones via the Cu(0)/Selectfluor
System-promoted Annulation of o-Aryl Chalcones 1
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