Rhodium(I)‐Catalyzed [2+2+2] and [4+2] Cycloadditions

The transition-metal-catalyzed [2+2+2] cycloaddition is a useful and atom-economical method for the construction of densely substituted six-membered frameworks. During the past 15 years, rhodium(I)-based catalysts are one of the most actively pursued catalysts for the [2+2+2] cycloaddition. In this chapter, the rhodium(I)-catalyzed [2+2+2] cycloaddition reactions of not only alkynes but also nitriles, heterocummulenes, alkenes, carbonyl compounds, and imines for the synthesis of six-membered carbocycles and heterocycles are disclosed. Additionally, the rhodium(I)-catalyzed [4+2] cycloaddition reactions and asymmetric variants of these [2+2+2] and [4+2] reactions are also described.