Visible-Light-Mediated Decarboxylative Thiocyanation of Cinnamic acids: An Efficient Photocatalytic Approach to the Synt
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Visible‑Light‑Mediated Decarboxylative Thiocyanation of Cinnamic acids: An Efficient Photocatalytic Approach to the Synthesis of (E)‑Vinyl Thiocyanates Deepali Jaiswal1 · Jyoti Tiwari1 · Shailesh Singh1 · Kartikey1 · Jaya Singh2 · Jagdamba Singh1 Received: 19 July 2020 / Accepted: 30 September 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract A simple and novel methodology for the synthesis of vinyl thiocyanates from decarboxylative cross-coupling reaction of cinnamic acids with KSCN under the synergistic interactions of visible light irradiation, Cs2CO3, Rose Bengal as the photocatalyst and air as the terminal oxidant at room temperature is reported. The reaction takes place by a radical pathway as evidenced from our experiments and literature. The report is the first example on the visible-light mediated thiocyanation of cinnamic acids, which employs environmentally benign and inexpensive starting materials and is characterized by easily removable by-product CO2. Graphic Abstract COOH
R
KSCN
1
2
Visible light, air CH3CN, r.t.
Cs2CO3 Rose Bengal
R -CO2
3 17 Molecules 12-85% Yield
SCN
Mild reaction conditions No transition- metal catalyst No strong oxidant Wide substrate scope
Keywords Visible light · Photoredox catalysis · C-S coupling · Radicals · Environmentally benign synthesis
1 Introduction Recently, visible-light-mediated decarboxylative crosscoupling reactions have emerged as an attractive strategy to construct C–C, C–P, C–S, C–O and C–N bonds [1–6]. The credit of such widespread recognition of the strategy Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10562-020-03414-6) contains supplementary material, which is available to authorized users. * Jagdamba Singh [email protected] 1
Environmentally Benign Synthesis Lab, Department of Chemistry, University of Allahabad, Allahabad 211002, India
Department of Chemistry, LRPG College, Sahibabad, Ghaziabad 201005, India
2
is linked with the potential advantages associated with it, e.g. environmental sustainability, cost-effectiveness, higher efficiency, greater selectivity and easily removable by-product [7–10]. Despite the great advances in the visible-lightmediated decarboxylative reactions, the formation of C–S bond via this strategy remains an underdeveloped process and deserves greater attention from the synthetic community [11, 12]. In synthetic organic chemistry, thiocyanation is a convenient method to form C-S bond [13–15]. In general, Pb(SCN)2, KSCN, NaSCN, AgSCN and N H4SCN salts are used as a SCN source to introduce the sulfur functionality to a substrate [16–21]. Thiocyanates, the product of this reaction, are valuable and versatile intermediates for the synthesis of sulfur containing heterocycles [22–25]. They also exhibit significant drug properties and biological activities, such as antifungal, antimicrobial and antiparasitic [26].
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In this context, significant efforts have been undertaken to
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