Oxidative Cyclization Based on Reversing the Polarity of Enol Ethers and Ketene Dithioacetals. Construction of a Tetrahydrofuran Ring and Application to the Synthesis of (+)-Nemorensic Acid

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• 作者：Bin Liu ; Shengquan Duan ; Angela C. Sutterer ; and Kevin D. Moeller
• 刊名：Journal of the American Chemical Society
• 出版年：2002
• 出版时间：August 28, 2002
• 年：2002
• 卷：124
• 期：34
• 页码：10101 - 10111
• 全文大小：271K
• 年卷期：v.124,no.34(August 28, 2002)
• ISSN：1520-5126

文摘

The utility of oxidative cyclization reactions for the construction of tetrahydrofuran rings has beenexamined. In these experiments, alcohol nucleophiles were found to be effective traps for radical cationintermediates generated from both enol ether and ketene dithioacetal groups. The reactivity of the alcoholtrapping group appeared to lie between that of an enol ether and an allylsilane trapping group. Thestereochemical outcome of cyclization reactions originating from the oxidation of an enol ether was foundto be controlled by stereoelectronic factors. The utility of these cyclization reactions was illustrated with thesynthesis of a key tetrahydrofuran building block for the synthesis of linalool oxide and rotundisine. Cyclizationreactions triggered by the oxidation of a ketene dithioacetal led to far greater levels of stereoselectivity.The stereochemical outcome of these reactions was shown to arise from steric factors involving the largerketene acetal group. The synthetic utility of cyclizations utilizing ketene dithioacetal derived radical cationswas demonstrated by completing an asymmetric synthesis of (+)-nemorensic acid. Finally, the reactionswere shown to be compatible with the use of an amide nucleophile and the direct formation of a lactoneproduct.