Alkynylations and Vinylations

Alkynes and alkenes are important building blocks in synthetic organic chemistry and related domains. Therefore, unceasing efforts have been invested to develop new methods to introduce these valuable functional groups. Traditionally, most alkynylation and alkenylation reactions have relied on the use of olefins and acetylenes as nucleophilic reacting species, limiting the accessible structural diversity. The discovery of the unique properties of hypervalent iodine has more recently significantly broadened the scope of electrophilic ethynylation and vinylation reactions. Alkynyl and alkenyl iodonium salts were first recognized as powerful reagents to install electrophilic acetylenes and olefins onto nucleophilic substrates under mild conditions. Their low stability has however narrowed the area of their applications. Since 2009, more stable cyclic benziodoxol(on)e reagents have shown their superiority as effective electrophilic alkynylating and alkenylating reagents in numerous metal-free and metal-catalyzed olefination and ethynylation reactions of carbon centered nucleophiles, radicals, and heteroatom nucleophiles. In this chapter, an overview of the progress in the field is presented, including a short summary of pioneering works, followed by a more in-depth description of recent results.