手性氮杂芳烃化合物因其在药物成分中的普遍性而极为重要。在此,通过铜( I)催化的 1, 4-二烯到 ( E )-β-取代的烯基氮杂芳烃。该反应在温和的质子转移条件下进行,具有很高的原子经济性。此外,该反应对 ( E )-α,β-不饱和氮杂芳烃具有广泛的底物范围,因为各种氮杂芳烃具有良好的耐受性,例如苯并噻唑、噻唑、N-甲基苯并咪唑、苯并恶唑、喹啉、异喹啉、嘧啶、吡嗪和三嗪。有趣的是,与 ( Z )-α,β-不饱和氮杂芳烃的反应以优异的结果提供了相同的产物,但具有相反的绝对构型。DFT 计算表明,形成 C-C 键的亲核加成是Z -/ E - 和对映体选择性的决定步骤,并为选择性的起源提供了基本原理。最后,通过烯烃复分解、[4+2]环化、[2+1]环化和苯并噻唑环的裂解等几个转化展示了产物的合成效用。
Regioselectivity in alkenyl(aryl)-heteroaryl Suzuki cross-coupling reactions of 2,4-dibromopyridine. A synthetic and mechanistic study
摘要:
2,4-Dibromopyridine undergoes a regioselective Suzuki cross-coupling reaction at position 2 with several alkenyl(aryl) boronic acids to render 4-bromo-2-carbon substituted pyridines, difficult to be prepared otherwise, in good yields under palladium catalysis, either Pd(PPh3)(4)/TlOH or Pd(2)dba(3)/PCy3/K3PO4 at 25 degrees C. This behavior is explained on the basis of the electrophilic character of both C-Br bonds, being their relative reactivity in 2,4-dibromopyridine similar to that in the corresponding monobromopyridines. In addition, the dicoupled compound 6 is not formed through a double oxidative addition of 2,4-dibromopyri dine to Pd(PPh3). (c) 2006 Elsevier Ltd. All rights reserved.