Cp*M-Catalyzed Direct Annulation with Terminal Alkynes and Their Surrogates for the Construction of Multi-Ring Systems

Abstract

Transition-metal-catalyzed C–H activation followed by oxidative cyclization with unsaturated coupling partners has been a valuable synthetic tool for the multiring molecular scaffolds. This Perspective introduces the recent progress on the Cp*M-catalyzed (M = Co, Rh, and Ir) oxidative direct annulation of functionalized arenes with terminal alkynes and their equivalents through C–H bond cleavage. The highlighted examples are categorized according to the 10 different types of reagents used in the transformations. The representative conditions, selected examples of the reaction scope, and key mechanistic aspects are briefly summarized.

Rhodium‐Catalyzed C−H Activation/Annulation of N‐Aryl‐pyrazolidinones with Vinylene Carbonate

“…In this realm, some convenient acetylene equivalents have been developed. [2] For example, vinyl acetate has been applied as acetylene equivalent for the construction of heterocycles, such as isoquinolones, isocoumarins, isoquinolines and indoles through transition-metal catalyzed CÀ H activations. [3] Recently, commercially available vinylene carbonate has beeb employed as an oxidizing acetylene surrogate in CÀ H activation, which can avoid the introducing of unexpected substituents into the newly formed structures.…”

Organocatalytic Synthesis of Substituted Vinylene Carbonates

“…Recently, vinylene carbonate has been mainly used as an acetylene [15] or ethynol [16] surrogate in annulation reactions [17] . Moreover, it was also demonstrated that it can act as an acetylation reagent in rhodium‐catalyzed cyclisation [18] .…”

Alkyne Surrogates in Cycloaddition Reactions for the Preparation of Molecules of Interest

“…The following discussion is structured according to the different types of cycloaddition reactions, i. e. (3+2), [4+2], and [2+2+2] cycloaddition reactions and is restricted to only one‐pot, two‐step cycloaddition/C=C bond formation processes. Related procedures which are not cycloaddition reactions [2] are out of scope of this review [3] …”