Fig. 3: Reaction development.

a Optimizing the reaction conditions. b Gram-scale preparation of Diels–Alder adduct 1 and its derivatization to advanced intermediates for further diversifications. c Late-stage diversifications of Diels–Alder products through sequential couplings of the latent groups. 1,2-DCE, 1,2-dichloroethane; BOX, bisoxazoline; Ph, phenyl; tBu, tert-butyl; NMO, N-methylmorpholine N-oxide; THF, tetrahydrofuran; PPTS, pyridinium p-toluenesulfonate.