The Squarate Ester-Polyquinane Connection. An Analysis of the Capacity of Achiral Divinyl Adducts To Rearrange Spontaneously to Polycyclic Networks Housing Multiple Stereogenic Centers

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• 作者：Leo A. Paquette and and Tina M. Morwick
• 刊名：Journal of the American Chemical Society
• 出版年：1997
• 出版时间：February 12, 1997
• 年：1997
• 卷：119
• 期：6
• 页码：1230 - 1241
• 全文大小：576K
• 年卷期：v.119,no.6(February 12, 1997)
• ISSN：1520-5126

文摘

The condensation of diisopropyl squarate and relatedcyclobutene-1,2-diones with 2 equiv of the samealkenyl anion or 1 equiv each of two different alkenyl anions can be avery effective method for the highlystereocontrolled synthesis of di-, tri-, and tetraquinanes. Tworeaction cascades have been identified. The mostprevalent and often exclusive reaction course is triggered by trans1,2-addition of the two nucleophiles. Twoconsecutive conrotatory processes subsequently arise to deliver adoubly charged eight-membered ring intermediate,protonation of which leads to transannular adolization. The secondoption begins with cis 1,2-addition, this eventtriggering structural reorganization via a dianionic oxy-Coperearrangement. When the alkenyl anions aresufficientlysubstituted, the two pathways are distinguishable on stereochemicalgrounds. A minor pathway consisting of trans1,4-addition is seen to operate in certain contexts, especially whenthe alkenyllithium is "soft". Acetylide anionscan also be utilized successfully; in such cases, the benefit ofregiocontrolled protonation surfaces and gives rise toa single product. Other aspects of these complex tandem reactionshave been investigated and are discussed.