Non‐Canonical Reactivity of Gold Carbene with Alkyne: An Overview of the Mechanistic Premise

• Published in: European journal of organic chemistry 2021-03, Vol.2021 (9), p.1321-1330
• Main Authors: Sancheti, Shashank P., Patil, Nitin T.
• Format: Article
• Language: English
• Subjects: Alkynes; Carbenes; Cations; Chemical reactions; Cyclopropenation; Gold; Gold carbenes; Gold catalysis; Interception; Metal carbenes; Reactivity; Transition metals; β-Gold vinyl cation
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.202001528

The unique nature of gold carbene and its synchronous counterpart gold‐stabilized carbocation, is mainly responsible for the non‐canonical reactivity profile that it demonstrates in comparison to any other transition metal carbene. Being an important subset to this class, reactions of gold carbene with alkyne sponsor products far more diverse than cyclopropenation as canonically expected in case of other transition metal carbenes. These gold‐catalyzed reactions have largely been proposed to follow either a [1,n]‐carbene transfer process or an alternate pathway involving a direct interception of the β‐gold vinyl cation with a nucleophile at the cationic carbon. Despite of a clear distinction in structure, bonding and energy of a vinyl gold carbene and β‐gold vinyl cation; they have been found to exhibit identical reactivities like cyclopropenation, C(sp2)–H insertion, etc. making it extremely difficult to “experimentally” investigate and validate a mechanistic pathway. It is because of lack of conclusive experimental evidence, in addition to the limited number of detailed computational studies, that multiple pathways have been proposed simultaneously to rationalize the product formation. As an effort to shed light on the mechanisms of these reactions, herein, documentation of these reactions with a focus on their mechanistic premise has been presented. Reactions of gold carbene with alkyne have been discussed with the emphasis on the possible mechanisms, while also focusing on the energetics of the key intermediates as studied in some of the crucial reports covered herein.