Crude extracts from the ginkgo tree, Ginkgo biloba, have been used for centuries to

Chapter 3, Problem 3.71

(choose chapter or problem)

Crude extracts from the ginkgo tree, Ginkgo biloba, have been used for centuries to alleviate symptoms associated with asthma. There are four principal components of Ginkgo extracts, called ginkgolide A, B, D, and M. During E. J. Coreys classic synthesis of ginkgolide B, compound 1 was converted into compound 5 (J. Am. Chem. Soc. 1988, 110, 649651): O O 3a O H3CO H3CO TfO Tf Tf N Tf N = S O O CF3 N Tf Li Li 1 2 4 6 5 3b + @ ! @ ! (a) Draw the resonance-stabilized anion (3) that is expected when compound 1 is treated with LDA (compound 2), which was introduced in 3.69. (b) Draw a mechanism for the conversion of 1 to 3 and explain why this step is irreversible. (c) Upon treatment with 4, anion 3 is converted into compound 5, and byproduct 6 is formed. Describe the factors that render 6 a particularly stable anion.