Nickel-Catalyzed Cycloaddition of 1,3-Dienes with 3-Azetidinones and 3-Oxetanones†

Both thermodynamic and kinetic forces make C–C bond activation one of the most difficult processes to facilitate.[1] Breaking the strong bond between two carbon atoms is further hampered by the increased steric congestion in C–C bonds relative to C–H and C–X bonds.[1a,b,2] Despite the difficulty associated with C–C bond activation, a handful of transition-metal-catalyzed methods have been developed.[1] In fact, these methods serve as potentially useful technology for the construction of complex molecular architectures from relatively simple starting materials in a highly atom-economical fashion. The C–C bond-activation step in these systems generally occurs by two important processes: 1) oxidative addition of the C–C bond to the transition metal, or 2) β-carbon elimination of transition-metal-alkyl complexes.[1a,j] Furthermore, the use of small cyclic systems wherein the release of inherent strain provides the necessary driving force for C–C bond cleavage has been a central theme of C–C bond activation strategies.[1,3,4]