Transition metal-catalyzed [2 + 2 + 2] cycloaddition of nitrogen-linked 1,6-diynes: a straightforward route to fused pyrrolidine systems

Transition metal-catalyzed [2 + 2 + 2] cycloadditions of nitrogen-linked 1,6-diynes with unsaturated motifs, such as alkynes, alkenes, nitriles, ketenes and isocyanates, have recently attracted more attention from synthetic organic chemists because of their high efficiency in the construction of numerous pyrrolidine based systems. Utilizing different chiral transition metal catalysts to access challenging chiral skeletons has been extensively explored in recent years. We hope to highlight the power of [2 + 2 + 2] cycloaddition chemistry to access a variety of fused pyrrolidine structures from inexpensive and easily available nitrogen-linked 1,6-diynes. The literature has been surveyed until the end of 2016.