Iodine catalysis: A green alternative to transition metals in organic chemistry and technology

Iodine and compounds of iodine in higher oxidation states have emerged as versatile and environmentally benign reagents for organic chemistry. One of the most impressive recent achievements in this area has been the discovery of catalytic activity of iodine in numerous oxidative transformations leading to the formation of new CO, CN, and CC bonds in organic compounds. These catalytic transformations in many cases are very similar to the transition metal-catalyzed reactions, but have the advantage of environmental sustainability and efficient utilization of natural resources. Iodine is an environmentally friendly and a relatively inexpensive element, which is currently underutilized in industrial applications. One of the main goals of this review is presenting to industrial researchers the benefits of using catalytic iodine in chemical technology as an environmentally sustainable alternative to transition metals. The present review summarizes catalytic applications of iodine and compounds of iodine in organic synthesis. The material is organized according to the nature of active catalytic species (hypoiodite, trivalent, or pentavalent hypervalent iodine species) generated in these reactions from appropriate pre-catalysts. Numerous synthetic procedures based on iodine(III) or iodine(V) catalytic species in the presence of hydrogen peroxide, Oxone, peroxyacids or other stoichiometric oxidants are summarized. A detailed discussion of catalytic cycles involving hypervalent iodine, hypoiodites, and other active intermediates is presented.