Hypervalent Iodine(III)-Mediated Cascade Cyclization of Propargylguanidines and Total Syntheses of Kealiinine B and C

An oxidative cascade cyclization of propargylguanidines promoted by phenyliodonium diacetate (PIDA) was developed. The protocol provides an efficient route for the synthesis of the alkaloids kealiinines B and C as well as homologues. The difference in the electronic nature of the acetylene substituent resulted in two ways of the cyclization. A plausible mechanism is proposed based on the experimental results. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim