A new approach to promoting sluggish Diels-Alder reactions: Dihapto-coordination of the diene
A new approach to promoting sluggish Diels-Alder reactions: Dihapto-coordination of the diene
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DOI：
10.1021/ja0553654
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发表时间：
2006-02-08
影响因子：
15
通讯作者：
Harman, WD
中科院分区：
文献类型：
--
作者：
Liu, WJ;You, F;Harman, WD
1，3-环己二烯与各种烯酮和烯烃(甲基乙烯基酮、乙基乙烯基酮、甲基丙烯连环)之间的环加成反应在室温下完成，产率在51%到68%之间，而不需要使用Lewis酸、高压或微波反应器。这种通常缓慢的环化反应是通过将二烯预先配位到π碱性钼络合物上来完成的。与η2结合的金属被认为促进了二烯和烯酮的未配位部分之间的迈克尔反应，生成的烯烃然后闭合形成环烯产品。有机环加合物可通过空气氧化或三氟化银氧化脱除，产率接近定量。对于空间位阻较大的烯酮(例如，均三甲氧甲酯)和甲基丙烯酸甲酯，想要得到的结果需要使用BF3·OEt2，并且产率要低得多(15−35%)
The cycloaddition between 1,3-cyclohexadiene and various enones and enals (methyl vinyl ketone, ethyl vinyl ketone, methacrolien) is accomplished at room temperature in yields ranging from 51 to 68% without the use of Lewis acids, high pressures, or microwave reactors. This normally sluggish cyclization is accomplished by precoordination of the diene to a π-basic molybdenum complex. The η2-bound metal is thought to promote a Michael reaction between the uncoordinated portion of the diene and the enone, and the resulting enolate then closes to form the cycloalkene product. The organic cycloadduct is removed by oxidation with air or with silver triflate in nearly quantitative yield. For more sterically hindered enones (e.g., mesityl oxide) and for methyl acrylate, the desired outcome requires the use of BF3·OEt2, and yields are significantly lower (15−35%)