Synthesis of Trifluoromethyl-Substituted Pyrazoles and 1,2,4-Triazines by Ring Transformation of Mesoionic 4-Trifluoroacetyl-1,3-oxazolium-5-olates with Phenylhydrazine
作者:Masami Kawase、Hiromi Koiwai
DOI:10.1248/cpb.56.433
日期:——
Mesoionic 4-trifluoroacetyl-1,3-oxazolium-5-olates 1 were easily prepared by the cyclodehydration reaction of N-acyl-N-alkyl-alpha-amino acids with trifluoroacetic anhydride. Due to the presence of the trifluoromethyl ketone and the mesoionic five-membered oxazole, there are three reaction sites to be attacked by the nucleophiles at C-2, C-5 and the trifluoroacetyl group in 1. Based on this model,
通过N-酰基-N-烷基-α-氨基酸与三氟乙酸酐的环脱水反应,可以容易地制备介电的4-三氟乙酰基-1,3-恶唑鎓-5-酸酯。由于三氟甲基酮和中性离子五元恶唑的存在,亲核试剂在C-1,C-5和三氟乙酰基上存在三个反应位点。基于该模型,三种模式发现苯肼的区域选择性攻击提供了三种不同的产物,分别以良好的产率提供了6-三氟甲基-1,2,4-三嗪3、3-三氟甲基-5-吡唑酮5和5-三氟甲基-3-羟基吡唑4。 ,取决于溶剂的性质和反应温度。