Pyridine Core Activation via 1,5-Electrocyclization of Vinyl Pyridinium Ylides Generated from Bromo Isomerized Morita-Baylis-Hillman Adduct of Isatin and Pyridine: Synthesis of 3-Spirodihydroindolizine Oxindoles

An activation of the pyridine nucleus has been achieved via 1,5-electrocyclization of vinyl pyridinium ylides generated from bromo isomerized Morita-Baylis-Hillman adducts of isatin and pyridine under basic conditions. The method has been successfully applied for an efficient synthesis of a number of 3-spirodihydroindolizine-2-oxindoles, which have been found as core structure of secoyohimbane and heteroyohimbane alkaloid natural products.