Brønsted Acid Catalyzed Carbocyclizations Involving Electrophilic Activation of Alkynes

Abstract

This review focuses on the carbocyclization reactions of alkyne-containing substrates catalyzed by Brønsted acids. The electrophilic activation occurs either by direct protonation of the alkyne or by formation of an intermediate cation that further reacts with the alkyne to give the vinyl cation key intermediate. A specific highlight will be put on the selectivity of the various methodologies described herein and on the mechanistic rationale.

Synthesis of cyclic silyl enol ethers from α-Aryl-α-diazoketones: new building blocks for preparation of indanones and α,β-unsaturated ketones

“…Vinyl cation species are regarded as distinctive and highly versatile intermediates in synthetic chemistry, making them an attractive option for utilization in organic synthesis. 1 The unique property of vinyl cation intermediates is their carbene-like reactivity, allowing them to participate in chemical bond insertion reactions. 2 For example, the C–H insertion reaction of vinyl cation intermediates is a valuable tool for constructing new C–C bonds and generating complex molecules.…”

Boron Trifluoride-Mediated Domino Dehydration/Electrophilic Cyclization of Silylalkynols Leading to 2,3-Fused Tricyclic Benzofulvenes

“…Overall, this domino dehydration/electrophilic cyclization process requires a stoichiometric BF 3 ·OEt 2 . Although the Brønsted acid-catalyzed carbocyclization involving electrophilic activation of alkynes is established, BF 3 ·OH 2 -catalyzed electrophilic cyclization of enynes has not been reported …”

Synthesis of Seven- and Eight-Membered Rings by a Brønsted Acid Catalyzed Cationic Carbocyclization of Biphenyl Embedded Enynes

“…In contrast, the involvement of nonstabilized carbocations is less well-explored, and the use of carbon-centered terminating groups is primarily limited to alkenes and arenes . In this context, carbocyclization of ortho -alkynylbiaryls by acetylene activation, using a stoichiometric amount of a Brønsted acid, and subsequent intramolecular addition of an arene, is well established (Scheme a). − Conversely, few examples of Brønsted acid catalyzed carbocyclizations of enynes in which the acetylene behaves as terminating group have been described . In these reactions, the carbocation generated by selective olefin protonation is captured by the alkyne, affording a vinyl carbocation.…”