An unexpected cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates to construct 2,3-dihydrobenzofuran spirooxindoles†
An unexpected Michael addition-inspired ring-opening/closure cascade reaction of 3-hydroxyoxindoles with coumarin-3-carboxylates was developed to access new dihydrobenzofuran or dihydrobenzothiophene spirooxindoles in 68–98% yields. This reaction not only provides an expedient and convenient method to assemble dihydrobenzofuran spirooxindoles, but also establishes a new reaction mode of coumarin-3-carboxylates. Moreover, it represents the first example of 3-hydroxyoxindoles serving as a C1 synthon possessing dual nucleophilic and electrophilic character with the hydroxyl group as a leaving group. Importantly, this methodology provides a rapid and robust approach to XEN907 analogues.