Recent Advances in the Synthesis of Iodoheterocycles via Iodocyclization of Functionalized Alkynes

Iodocyclization reactions are acquiring an increasing importance in organic synthesis, in view of the possibility to obtain iodine- containing heterocycles starting from readily available acyclic substrates under mild reaction conditions. Various aspects of these iodocyclization reactions have been recently reviewed, including the application of iodocyclization processes to the synthesis of natural products, heterocyclic derivatives, and carbocyclic derivatives, as well as the construction of heterocyclic libraries. The present mini-review is intended to highlight some very recent (from 2010 to the beginning of 2013) and particularly interesting examples of the synthesis of heterocyclic derivatives by the iodoheterocyclization of functionalized alkynes. The iodoheterocyclization of acetylenic substrates bearing a suitably placed nucleophilic group is a powerful method for the direct synthesis of unsaturated iodine-containing heterocycles. The products obtained can be further elaborated through various cross-coupling reactions (such as Heck, Suzuki-Miyaura, and Sonogashira reactions), making the process of particular synthetic interest. Moreover, the iodocyclization reaction is carried out under very mild reaction conditions (generally room temperature), using a simple source of electrophilic iodine, such as I-2, ICl, or NIS (N-iodo-succinimide), usually in the presence of a base to help buffer the acid produced by deprotonation of the nucleophilic functional group present in the substrate. The mini-review is divided into three parts: Synthesis of iodine-containing oxygen heterocycles; Synthesis of iodine-containing nitrogen heterocycles; and Synthesis of iodine-containing sulfur and selenium heterocycles. The examples shown in the mini-review demonstrate that the iodoheterocyclization of functionalized alkynes is a wide-scope synthetic methodology, which can also be useful for the synthesis of biologically active molecules and complex natural products.