Metal-free visible-light-promoted intermolecular [2+2]-cycloaddition of 3-ylideneoxindoles

Article abstract of DOI:10.1016/j.tet.2017.02.035

The Rose Bengal sensitized intermolecular [2?+?2]-cycloaddition of 3-ylideneoxindoles for the synthesis of spirocyclic oxindoles was developed successfully under visible light irradiation conditions. The cycloaddition products were obtained in good yields

Full text of DOI:10.1016/j.tet.2017.02.035

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Metal-free visible-light-promoted intermolecular [2+2]-cycloaddition of 3-
ylideneoxindoles
Ling-Ling Wu, Gao H. Yang, Zhi Guan, Yan-Hong He
PII:
S0040-4020(17)30174-6
10.1016/j.tet.2017.02.035
TET 28476
DOI:
Reference:
To appear in: Tetrahedron
Received Date: 24 January 2017
Revised Date: 15 February 2017
Accepted Date: 17 February 2017
Please cite this article as: Wu L-L, Yang GH, Guan Z, He Y-H, Metal-free visible-light-promoted
intermolecular [2+2]-cycloaddition of 3-ylideneoxindoles, Tetrahedron (2017), doi: 10.1016/
j.tet.2017.02.035.
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Graphical Abstract

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Metal-free visible-light-promoted intermolecular [2+2]-cycloaddition
of 3-ylideneoxindoles
Ling-Ling Wua, Gao H. Yangb, Zhi Guana,* and Yan-Hong Hea,*
a Key Laboratory of Applied Chemistry of Chongqing Municipality, School of Chemistry and Chemical
Engineering, Southwest University, Chongqing 400715, PR China
b Chemistry Department, College of Saint Benedict and Saint John’s University, MN 56374, USA
E-mails: guanzhi@swu.edu.cn (for Z. Guan); heyh@swu.edu.cn (for Y.-H. He)
Abstract: The Rose Bengal sensitized intermolecular [2+2]-cycloaddition of 3-ylideneoxindoles
for the synthesis of spirocyclic oxindoles was developed successfully under visible light
irradiation conditions. The cycloaddition products were obtained in good yields (up to 93%) with
excellent diastereoselectivity and regioselectivity by using a low loading of Rose Bengal (0.125
mol%) as a triplet sensitizer. This work demonstrates the potential benefits of Rose Bengal in
visible light catalysis.
Key words: visible light; Rose Bengal; 3-ylideneoxindoles; [2+2]-cycloaddition; spirocyclic
oxindoles
1. Introduction
Among many green chemical approaches, visible light photocatalysis can serve as a valuable
application since light can be considered as an ideal reaction condition for environmentally
friendly and green chemical synthesis.1 Using visible light and either ruthenium or iridium
1

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complexes as photosensitizers2, 3e have been reported for the formation of fundamental and useful
chemical transformations3. However, the potential toxicity and the limited availability of the
ruthenium or the iridium salts hinder the production of fine chemicals and pharmaceuticals.4
Organic dyes could serve as promising catalysts in the field of visible light-induced reactions due
to their high absorption within the visible spectrum.5 Moreover, they are inexpensive, low toxic,4a,
6 and widely available. For example, commercially readily available Rose Bengal presents a viable
alternative to inorganic photocatalysts.7 The photocatalytic activity of Rose Bengal is similar to
ruthenium or iridium complexes in some reactions such as alkylation reaction,4a photoredox
oxidative reaction,4b, 6b, 7b, 8 oxyamination reaction,9 sulfoxidation reaction10 and thiocyanation
reaction.11 In consideration of the advantages of Rose Bengal as a photosensitizer in visible light
catalysis, it is necessary to further explore its application in the field of photocatalysis.
Spirocyclic oxindoles have emerged as attractive synthetic targets in chemical science
because they are widespread in the bioactive alkaloids and pharmacologically important
compounds.12 They display various biological activities and have been exploited as insecticidal,
antitumor and antibacterial agents.13 For this reason, this family of oxindole has been extensively
researched.14 A number of synthetic methods have been developed in pursuit of this kind of
structure, including rearrangements,15 cascade Michael-aldol reactions,16 conjugate additions,17
cycloadditions18 et al. Although considerable progress has been described toward their synthesis,
the potential biological activities of spirocyclic oxindole skeleton have led to a demand for
efficient and novel synthetic methods.
Since Ciamician et al. reported the first example of a photoinitiated intramolecular [2+2]
enone cycloaddition in 1908,19 some research groups have further reported [2+2] cycloaddition
2