Chemistry of Tonghaosu Analogs: Novel Acid‐Catalyzed Nucleophilic Addition to the Dienyl Acetal System
The acid-catalyzed nucleophilic addition reaction of spiroketal enol ether-containing tonghaosu analogs 2 was explored. Soft nucleophiles, such as mercaptans, alcohols and heteroaromatic compounds, gave rise exclusively to 1,6-adducts, while harder nucleophiles, such as Grignard reagents, afforded mixtures of 1,2- and 1,6-adducts. The reaction with cysteine and glutathione, which might be related to the mode of action of insect antifeeding, also took place smoothly. Friedel−Crafts dimerization reactions of 10 and 11 gave the dimers 12 and 13 respectively. By comparison of 1H NMR spectroscopic data, we also suggest that the structure of compound 9 reported in the literature for a natural product is revised to that of compound 13. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)