New conformationally flexible and recyclable aryl iodine catalysts from inexpensive chiral source for asymmetric oxidations

Abstract

Despite the remarkable advances in the research field of asymmetric catalytic oxidation reactions via hypervalent iodines with simple procedures, high level of efficiency and stereoselectivity over the past few decades, the development of their highly scalable, environmentally benign, and sustainable protocols under the greener organocatalysis paradigm for further industrial translations remains a long-standing synthetic organic chemistry and process engineering challenge. Herein, we design and synthesize a new library of conformationally flexible and recyclable aryl iodine catalysts by utilization of (i) industrial waste (chloramphenicol base) as the scaffold and (ii) inexpensive amino acid residue (threonine) as the chiral source. Our chiral aryl iodine(III) catalysts bearing H-bond donors and a tunable chiral pocket have been successfully applied in diverse robust asymmetric oxidative transformations, e.g., dearomatization, spirolactonization, direct C(sp2)−H/C(sp3)−H cross-coupling, and fluoridation. Our processes feature a column-isolation-free approach, easy-handling operation, and upscaling synthesis, with the catalysts being facilely recycled in particular via precipitation.