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. Corey’s classic synthesis of ginkgolide B, compound 1 was converted into compound 5 (J. Am. Chem. Soc. 1988, 110, 649–651):
(a) Draw the resonance-stabilized anion ( 3) that is expected when compound 1 is treated with LDA (compound 2), which was introduced in Problem 3.69.