Stepwise Acid-Promoted Double-Michael Process: An Alternative to Diels−Alder Cycloadditions for Hindered Silyloxydiene−Dienophile Pairs
摘要:
The hindered diene 1 reacts with 3-methylcyclohexenone 6 catalyzed by triflimide to produce the Mukaiyama Michael product 7 (low-temperature quenching) or the [4+2] cycloadduct 8 (quenching at 0 degrees C). Reaction of the hindered diene 23 with 2-methylcyclohexenone 12 with 5:1 AlBr3:AlMe3 afforded a 71% yield of a 1.9:1 mixture of two cycloadducts. Hydrolysis of the major isomer gave the dione 27', a model for the BCD ring system of pentacyclic triterpenes.
Synthesis of 2-Substituted 7-Hydroxybenzofuran-4-carboxylates via Addition of Silyl Enol Ethers to <i>o</i>-Benzoquinone Esters
作者:Michael E. Jung、Felix Perez
DOI:10.1021/ol900416x
日期:2009.5.21
Mukaiyama Michael addition of silyl enol ethers 13 to the 1,2-quinone-4-carboxylate 6 (formed in situ by oxidation of the catechol ester 8) afforded the 2-subsituted 7-hydroxybenzofuran-4-carboxylates 14 in fair to good yields. Alkyl and aryl systems work well, but highly electron-rich silyl enol ethers could not be used because of competing oxidation.
Mukaiyama Michael 将甲硅烷基烯醇醚13加成到 1,2-醌-4-羧酸酯6(通过儿茶酚酯8的氧化原位形成)提供了 2-取代的 7-羟基苯并呋喃-4-羧酸酯14,收率一般到良好. 烷基和芳基体系工作良好,但由于竞争氧化,不能使用高度富电子的甲硅烷基烯醇醚。