[4 + 1] annulation reaction of cyclic pyridinium ylides with in situ generated azoalkenes for the construction of spirocyclic skeletons

摘要

Two new types of cyclic pyridinium ylides were designed and further used in reactions with azoalkenes to access structurally diverse spirocyclic compounds. A range of spiropyrazoline oxi-ndoles could be smoothly obtained in up to 99% yield via a [4 + 1] annulation process with oxindole 3-pyridinium ylides as C1 syn-thons. Similarly, a series of spiropyrazoline indanones could be prepared with indanone 2-pyridinium ylides as Cl synthons. This work represents the first example of cyclic pyridinium ylides as Cl synthons for the efficient construction of spirocyclic compounds.