Synthesis of Chiral Building Blocks for Oxygenated Terpenoids through a Simultaneous and Stereocontrolled Construction of Contiguous Quaternary Stereocenters by an Ireland–Claisen Rearrangement

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• 作者：Yoshihiro Akahori ; Hiroyuki Yamakoshi ; Yuki Sawayama ; Shunichi Hashimoto ; Seiichi Nakamura
• 刊名：Journal of Organic Chemistry
• 出版年：2014
• 出版时间：January 17, 2014
• 年：2014
• 卷：79
• 期：2
• 页码：720-735
• 全文大小：703K
• ISSN：1520-6904

文摘

Methods for highly stereocontrolled syntheses of chiral building blocks with a triad of contiguous stereocenters, including two quaternary ones, have been developed. Ireland鈥揅laisen rearrangement of the (Z)-silyl ketene acetal generated stereoselectively from the (R)-3-methylcyclohex-2-enyl ester derived from an acyclic carboxylic acid proceeded through a chairlike transition state to give the rearranged product with an S configuration at the position 伪 to the carboxyl group. Introduction of a cyclic conformational constraint in the acid component completely switched the transition state of the rearrangement to a boatlike one, leading to the predominant formation of a product with an R configuration, from which pseudodiastereomeric 伪-hydroxy esters were obtained in a four-step sequence. The enyne obtained through a base-mediated double eliminative ring-opening reaction was successfully converted into advanced intermediates for the synthesis of 9-oxygenated labdane diterpenoids through a Heck reaction and a regioselective transformation of the resultant diene.