Eosin Y Catalyzed Visible-Light-Promoted Aerobic Oxidative Cyclization of 2-Aminobenzothiazole

Abstract

A mild and efficient one-pot visible light irradiated synthesis of 2-aminobenzothiazole 4(a-l) from arylisothiocyanate 1(a-l) and secondary amines 2 have been reported in presence of eosin Y as an organophotoredox catalyst at room temperature under aerobic condition. This synthesis includes application of air and visible light as inexpensive, readily available, high atom economy, non-toxic and sustainable regents.

Eosin Y catalysed photoredox synthesis: a review

“…A plausible mechanism involving photoredox catalysis for the oxidative cyclization of N-arylthioureas is depicted in Scheme 22. 24 On absorption of visible light, the organophotoredox catalyst eosin Y (EY) is excited to its singlet state 1 EY* which through inter system crossing (ISC) comes to its more stable triplet state 3 EY* and undergoes a single electron transfer (SET). 3 EY* may undergo both reductive and oxidative quenching.…”

“…Recently, a superior alternative to transition metal photoredox catalysts, especially metal-free organic dyes particularly eosin Y has been used as economically and ecologically superior surrogates for Ru(II) and Ir(II) complexes in visible-light promoted organic transformations involving SET [18][19][20][21] (single electron transfer). These organic dyes have got much more attention with the last few years also due to easy handling, eco-friendly and have great potential for applications in visible-light-mediated organic synthesis [22][23][24] which fulls the basic principle of green chemistry. In this article, we discuss recent applications of eosin Y as a visible light photocatalyst in organic synthesis.…”

Construction and Functionalization of Heteroarenes by Use of Photoredox Catalysis

“…The catalytic photooxidation of an amine group led to the formation of the corresponding nitrogen‐centered radical, which was able to cyclize to generate the fused indazole ring. Similar heteroatom oxidation through single‐electron transfer has also been reported in the synthesis of benzothiazole and aminobenzothiazole derivatives …”

Photocatalytic formation of carbon–sulfur bonds

“…In the same year, the group of Singh published two similar, but metal-free procedures. In the first report a new photocatalyzed procedure for the preparation of 2-aminobenzothioazoles from the respective N -aryl thioureas with Eosin Y as photoredox catalyst and molecular oxygen as terminal oxidant was shown ( Scheme 33 ) [ 68 ]. They propose a mechanism where the excited state of Eosin Y is quenched reductively by the deprotonated thiourea derivative giving the Eosin Y radical anion and a thiyl radical.…”