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

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.本研究报道了一系列多环芳香基-N-乙氧羰基硫代酰胺S-氧化物的合成，以及三氟甲磺酸（triflic acid）促进其环化生成噻吩亚胺稠合芳烃的反应，目标产物包含2H-萘并[1,8-bc]噻吩-2-亚胺、3H-芘并[10,1-bc]噻吩-3-亚胺、4H-芘并[1,10-bc]噻吩-4-亚胺、3H-芘并[10,1-bc]噻吩-3-亚胺、4H-芘并[1,10-bc]噻吩-3-亚胺、3H-芘并[10,1-bc]噻吩-3-亚胺以及4H-苝并[3,4-bc]噻吩-4-亚胺核心结构。所提出的反应机理涉及一类新型亲电硫活性中间体，即质子化亚胺基亚磺酸或亚胺硫鎓阳离子。此类中间体可进攻芳烃的peri位与ipso位，部分反应会生成区域异构体产物。该反应以高收率得到新型多环荧光团，其发射波长范围为500~606 nm，量子产率介于0.025~0.64之间。通过与母体芳烃对比可知，该稠合亚胺噻吩结构单元可使产物的吸收与发射光谱带产生显著红移。