An Alkylidene Carbene C–H Activation Approach toward the Enantioselective Syntheses of Spirolactams: Application to the Synthesis of (−)-Adalinine

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• 作者：Krishna Annadi ; Andrew G. H. Wee
• 刊名：Journal of Organic Chemistry
• 出版年：2016
• 出版时间：February 5, 2016
• 年：2016
• 卷：81
• 期：3
• 页码：1021-1038
• 全文大小：834K
• ISSN：1520-6904

文摘

A method based on in situ alkylidene carbene generation-C–H insertion reaction of 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones is developed for the enantioselective synthesis of 1-azaspiro[4,4]non-6-ene-2-ones and 6-azaspiro[4,5]dec-1-ene-7-ones. The required 5-(3-oxobutyl)pyrrolidin-2-ones and 6-(3-oxobutyl)piperidin-2-ones are prepared from the Wacker oxidation of internal alkenes typified by 5-(but-2-enyl)pyrrolidin-2-ones and 6-(but-2-enyl)piperidin-2-ones, respectively. Excellent regioselectivity (≥92:8) is realized for the Wacker oxidation, and high yields (78–89%) of the desired lactam ketones are obtained. The results from further investigations into the Wacker oxidation suggested that the high regioselectivity of the oxidation in these lactam alkenes might be due to the participation of the lactam nitrogen via intramolecular coordination to Pd(II) during the reaction. Studies on alkylidene carbene generation-C–H insertion reaction of the lactam ketones revealed that the reaction efficiency is sensitive to the reaction temperature and the amount of lithio(trimethylsilyl)diazomethane employed, which led to the development of optimal reaction conditions for effecting alkylidene carbene generation-C–H insertion. Using the optimal reaction conditions, good to high yields (53–76%) of both γ- and δ-lactam spirocycles were obtained. The synthetic utility of the spirolactams was demonstrated by the synthesis of (?)-adalinine.