Cascade Michael Addition/Cycloketalization of Cyclic 1,3-Dicarbonyl Compounds: Important Role of the Tethered Alcohol of 伪,尾-Unsaturated Carbonyl Compounds on Reaction Rate and Regioselectivity
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- 作者：Hongliang Yao ; Liyan Song ; Yuan Liu ; Rongbiao Tong
- 刊名：Journal of Organic Chemistry
- 出版年：2014
- 出版时间：September 19, 2014
- 年：2014
- 卷：79
- 期：18
- 页码：8774-8785
- 全文大小：708K
- ISSN：1520-6904
文摘
Reactions of 伪,尾-unsaturated aldehydes and cyclic 1,3-dicarbonyl compounds proceed primarily by cascade Knoevenagel condensation/six-蟺-electron electrocyclization (K6EC, formal [3 + 3] cycloaddition), while 伪,尾-unsaturated ketones usually react with cyclic 1,3-dicarbonyl compounds in a 1,4-addition manner. This paper discloses our findings that under acidic conditions, 伪,尾-unsaturated carbonyl compounds (ketones and aldehydes) with a tethered alcohol react with cyclic 1,3-dicarbonyl compounds in a highly regioselective 1,4-addition fashion via in situ generation of a hypothetical 伪-methylene cyclic oxonium ion as the reactive Michael acceptor. Our studies uncovered the important effect of the tethered alcohol on the reaction rate and/or efficiency and some new mechanistic aspects of the cascade Michael addition/cycloketalization. Finally, the substrate scope was examined, and 43 analogues of penicipyrone and tenuipyrone were prepared in good to excellent yields.