Reactions of 2‐Amino‐1,3‐butadienes and Fischer Alkynyl Carbenes: Up to Nine C−C Bonds and Seven Stereogenic Centers Created in a Stereoselective Manner through a Cascade Process

New reactions of alkynylcarbene complexes with 2-amino-1,3-dienes are reported. The reactions involve a first [4+2] cycloaddition step followed by a cyclopentannulation process that generates a molecule containing a cyclopentadiene moiety capable of undergoing a new [4+2] cycloaddition reaction with the carbene complex. The process can be controlled to produce one, two or three cycloaddition–cyclopentannulation cycles (see Equation) in order to synthesize molecules from fluorenes to complex polycyclic scaffolds.