Elemental Selenium in the Synthesis of Selenaheterocycles

An overview of the known methods of introducing selenium under the action of elemental selenium into the structures of various saturated, unsaturated, and heteroaromatic selenacycles containing C-Se, N-Se, B-Se, Ge-Se and P-Se bonds is presented. These methods include metal, iodine, bromine or chlorine exchange for selenium and the direct cyclization of 1-(2-bromoaryl)benzimidazoles, polyunsaturated hydrocarbons, acetylenes, propargylic amines, 3-halogenaryl amides, aryl amides, diazo-compounds, 2-aminoacetophenone, and the annulation of ethynyl arenes. Three- and four-component reactions utilizing elemental selenium as one of the components and leading to selenium-containing heterocycles are presented as well.