Panda Niranjan, Mattan Irshad
Department of Chemistry, National Institute of Technology Rourkela Odisha-769008 India
RSC Adv. 2018 Feb 16;8(14):7716-7725. doi: 10.1039/c7ra12419h. eCollection 2018 Feb 14.
An efficient protocol for the synthesis of various coumestans from the intramolecular annulation of 3-iodo-4-aryloxy coumarins through C-H activation has been developed. When 3-iodo-4-aryloxy coumarins were treated with 10% Pd/C (0.3 mol% Pd) in the presence of sodium acetate, the corresponding coumestans were produced in good to excellent yield. Reusability of the palladium catalyst was investigated in up to three consecutive cycles and it was found that the yield of the reaction was almost unaltered. Sequential iodination and -arylation of 4-hydroxy coumarins leading to the 3-iodo-4-aryloxy coumarins were also achieved in a one-pot two-step process starting from aryl iodides in high yield. Pivalic acid was revealed to be the most effective additive for the later method to produce 3-iodo-4-phenoxy coumarins. Different functional groups bearing electron-donating as well as withdrawing groups are also tolerant to the reaction conditions.
已开发出一种通过C-H活化由3-碘-4-芳氧基香豆素分子内环化合成各种香豆雌酚的有效方案。当3-碘-4-芳氧基香豆素在乙酸钠存在下用10% Pd/C（0.3 mol% Pd）处理时，相应的香豆雌酚以良好至优异的产率生成。对钯催化剂的可重复使用性进行了多达三个连续循环的研究，发现反应产率几乎没有变化。从芳基碘开始，通过一锅两步法也以高产率实现了4-羟基香豆素的顺序碘化和芳基化，从而得到3-碘-4-芳氧基香豆素。新戊酸被证明是后一种方法生产3-碘-4-苯氧基香豆素最有效的添加剂。带有供电子基团和吸电子基团的不同官能团也耐受该反应条件。
