Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda 669-1337, Japan.
Molecules. 2021 Nov 19;26(22):7008. doi: 10.3390/molecules26227008.
TiCl (or SnCl)-promoted hetero-type benzannulation reactions using various (2,2-dichlorocyclopropyl)(thiophen-2-yl)methanols proceeded smoothly to produce uniquely substituted 4-chlorobenzothiophenes (five examples). The present approach involves the first distinctive thiophene formation from thiophene cores, in contrast to traditional methods of thiophene formation from benzene cores. The stereocongested (less reactive) Cl position in the obtained 4-chlorobenzothiophenes functioned successfully as the partners of three cross-coupling reactions: (i) a Suzuki-Miyaura cross-couplings using Pd(OAc)/SPhos/KPO catalysis (seven examples; 63-91%), (ii) a hydroxylation using KOH/Pd(dba)/tBu-XPhos catalysis (85%), and (iii) a borylation using a B(pin)/Pd(dba)/XPhos/NaOAc catalysis-provided 4-(pin)B-benzothiophene (58%).
TiCl（或 SnCl）促进的各种（2,2-二氯环丙基）（噻吩-2-基）甲醇的杂芳族苯并环化反应顺利进行，生成独特取代的 4-氯苯并噻吩（五个实例）。本方法涉及从噻吩核首次形成独特的噻吩，与传统的从苯核形成噻吩的方法形成对比。所得到的 4-氯苯并噻吩中立体拥挤（反应性较低）的 Cl 位置成功地作为三种交叉偶联反应的偶联伙伴：（i）使用 Pd(OAc)/SPhos/KPO 催化的 Suzuki-Miyaura 交叉偶联反应（七个实例；63-91%），（ii）使用 KOH/Pd(dba)/tBu-XPhos 催化的羟基化反应（85%），以及（iii）使用 B(pin)/Pd(dba)/XPhos/NaOAc 催化的硼化反应-提供 4-（pin）B-苯并噻吩（58%）。
