Polycyclic Aromatic N-Ethoxycarbonyl Thioamide S-Oxides and Their Triflic Acid Promoted Cyclization to Fluorescent Thiophene Imine-Fused Arenes

Abstract

We present the synthesis of a series of polycyclic aromatic-N-ethoxycarbonylthioamide S-oxides and their triflic acid-promoted cyclization to thiophene imine-fused arenes having 2H-naphtho[1,8-bc]thiophen-2-imine, 3H-pyreno[10,1-bc]thiophen-3-imine, 4H-pyreno[1,10-bc]thiophen-4-imine, 3H-pyreno[10,1-bc]thiophen-3-imine, 4H-pyreno[1,10-bc]thiophen-3-imine, 3H-pyreno[10,1-bc]thiophen-3-imine, and 4H-peryleno[3,4-bc]thiophen-4-imine cores. The proposed reaction mechanism involves the intermediacy of a novel type of electrophilic sulfur species, namely protonated iminosulfenic acid or iminosulfenium cations. These species may attack the peri- or ipso-position of the arene, leading in some cases to regioisomeric products. The reaction affords in high yields novel polycyclic fluorophores emitting in the range of 500-606 nm with quantum yields of 0.025-0.64. Comparison with the parent arenes reveals that the fused iminothiophene moiety brings about significant bathochromic shifts of the absorption and emission bands.

Recent Advances in Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds

“…Perylene was selectively derivatized in a 3-position in an S E Ar reaction with ethoxycarbonyl isothiocyanate in the presence of triflic acid to provide 93.1 ( Scheme 93 , see Scheme 142 , Section 4.4 , for related fused pyrenes). 192 Oxidation to thioamide S- oxide 93.2 and subsequent cyclization under acidic conditions provided 93.3 in very high yield (95%). The thiophene-imine-fused perylene 93.3 was strongly emissive in DCM solution, with the emission maximum at 606 nm and a quantum yield of 54%.…”

“…In 2018, Zakrzewski and co-workers developed a TfOH-promoted cyclization method of polycyclic aromatic N -ethoxycarbonylthioamide S -oxides, which provides pyrenes with a [ cd ]fused thiophene imine unit ( Scheme 142 , see Scheme 93 , Section 3.4 , for perylene analogues). 192 The proposed reaction mechanism involves the intermediacy of an electrophilic sulfur species, either a protonated iminosulfenic acid or an iminosulfenium cation. These species may attack either the peri - or ipso -position of the arene, leading to regioisomeric products like 142.2b and 142.2b′ .…”

Chemoselective Ullmann Reaction of α-Trisubstituted Thioamides: Synthesis of Novel 2-Iminobenzothiolanes

“…Therefore, several elegant synthetic methods have been developed for the construction of 2-aminobenzothiophene derivatives, whereas those for the 2-iminobenzothiophene core remain elusive in the literature. , Recently, a 2-iminothiophene-fused polyaromatic compound A were synthesized from thioamides (Figure ). The photophysical studies show emission in the range of 500–606 nm with quantum yields up to 0.64 . Hence, compound A has been considered a potential core for developing optical device materials.…”

“…8,9 Recently, a 2iminothiophene-fused polyaromatic compound A were synthesized from thioamides (Figure 1). 10 The photophysical studies show emission in the range of 500−606 nm with quantum yields up to 0.64. 10 Hence, compound A has been considered a potential core for developing optical device materials.…”

Transition metal-free, chemoselective arylation of thioamides yielding aryl thioimidates orN-aryl thioamides

“…Thioamides and their aryl thioimidate derivatives are important units in bioactive molecules, and in intermediates towards such compounds. 1 The thioimidate moiety can also be found in heterocycles such as thiazoles and benzothiazoles, 2 and in early stage solar absorbers. 3 The aryl thioimidate scaffold has also been shown to regioselectively react with alkynes to give aryl thio azadienes.…”