Chalcogen Bonding Activates [1.1.1]Propellane: Constructing Spiro[3.3]heptanes via Cyclobutyl Insertion into...

Chalcogen bonding catalysis has recently emerged as a new platform in organic synthesis, enabling the achievement of a diverse array of reactions. All of these chalcogen bonding catalyzed reactions rely on the interactions with lone-pair and π electrons. Owing to the lack of effective interaction with σ electrons, the activation of C-C σ-bonds by chalcogen bonding catalysts remains one of the most noteworthy unrealized challenges in this field. Here, we describe the activation of the C-C σ-bond of [1.1.1]propellane by chalcogen bonding, enabling the insertion of a cyclobutyl moiety into cyclopropenones to construct spiro[3.3]heptanes. Conventionally, the activation of the C-C σ-bond of [1.1.1]propellane was enabled by transition metals; however, the previously active transition-metal catalysts were ineffective in facilitating the insertion reaction between [1.1.1]propellane and cyclopropenones. While the activation of the C-C σ-bond of [1.1.1]propellane by the main-group catalyst is elusive, conversely, this research relies on using chalcogen bonding to activate [1.1.1]propellane and to stabilize the alkyl carbene intermediate. Mechanistic investigation suggests that a dual catalysis mode is operative. This method is highly efficient, and the reactions were generally completed within several minutes to give spiro[3.3]heptanes using 2.5 mol % catalyst at 0 °C or room temperature.