Substituent Effect of Imino-<i>O</i>-arenesulfonates, a Coupling Partner in Suzuki–Miyaura Reaction for Substitution of the Pyrazine Ring: A Study for the Synthesis of Coelenterazine Analogs
作者:Arthit Makarasen、Masaki Kuse、Toshio Nishikawa、Minoru Isobe
DOI:10.1246/bcsj.82.870
日期:2009.7.15
Amino(aryl)pyrazines, a key intermediate in the synthesis of coelenterazine and its analogs, can be prepared in excellent yields by utilizing imino-O-tosylates in the Suzuki–Miyaura reaction. These imino-O-tosylates serve as a substitute for the corresponding imino-O-triflates, which are sometimes too unstable to be stored during the optimization of the reaction conditions. Aryltrifluoroborates, a coupling partner, worked well when arylboronic acids or arylboronate esters were less reactive. Aryltrifluoroborates also worked well when containing an electron-donating group attached to the aromatic ring. The study of the substituent effect of imino-O-arenesulfonates demonstrated a major difference in the rate of the reactions when changing from electron-donating groups to electron-withdrawing groups at the para position of arenesulfonates. Imino-O-arenesulfonate containing a para-bromo substituent only gave the desired coupling product leaving the para substituent of arenesulfonate untouched.
氨基(芳基)吡嗪是合成海葵素及其类似物的重要中间体,可以通过利用亚胺-O-托磺酸酯在铃木–宫浦反应中以优良的收率制备。这些亚胺-O-托磺酸酯作为相应的亚胺-O-三氟甲烷磺酸酯的替代品,后者在反应条件优化过程中有时过于不稳定而无法储存。当芳基硼酸或芳基硼酸酯的反应活性较低时,芳基三氟硼酸盐作为耦合伙伴表现良好。含有电子给体基团的芳基三氟硼酸盐在反应中也表现良好。对亚胺-O-芳烃磺酸盐取代基效应的研究表明,在替换亚胺-O-芳烃磺酸盐对位的电子给体基团与电子吸引基团时,反应速率存在显著差异。含有对溴取代基的亚胺-O-芳烃磺酸盐仅给出了所需的耦合产物,而未触及芳烃磺酸盐的对位取代基。