Herein we report a one-step, catalytic, Markovnikov-selective, and scalable method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. Powerful catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by extensive optimization of the reaction conditions and tuning of the thioester unit. This is a rare instance of thioesters showing nucleophilic behavior. This method was also applicable to alkenyl selenoesters.

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>

<div>We report here a catalytic, Markovnikov selective, and scalable synthetic method for the synthesis of saturated sulfur heterocycles, which are found in the structures of pharmaceuticals and natural products, in one step from an alkenyl thioester. Unlike a potentially labile alkenyl thiol, an alkenyl thioester is stable and easy to prepare. The powerful Co catalysis via a cobalt hydride hydrogen atom transfer and radical-polar crossover mechanism enabled simultaneous cyclization and deprotection. The substrate scope was expanded by the extensive optimization of the reaction conditions and tuning of the thioester unit.</div>