Tropylium Ion Catalyzes Hydration Reactions of Alkynes

Abstract

The hydration of alkynes is one of the most atom‐economic and versatile synthetic protocols to access carbonyl compounds. This fundamental reaction, however, often requires transition‐metal catalysts or harsh reaction conditions to promote the addition of water to the carbon–carbon triple bond. In this work, it is demonstrated that the non‐benzenoid aromatic tropylium ion can be used as an organic Lewis acid promoter for the hydration of alkynes under simple reaction conditions with excellent outcomes.

Accelerated Metal-Free Hydration of Alkynes within Milliseconds in Microdroplets

“…By functionalizing the sulfonic acid group with imidazole-based ionic liquids, the hydration reaction of alkynes can proceed at relatively low temperature (∼60 °C), and the Brønsted acid ionic liquids can be reused as catalysts without catalytic loss . A Lewis-acid-catalyzed hydration reaction also has been reported, where the nonbenzenoid aromatic tropylium ion as an organic Lewis acid can be used to promote the hydration of alkynes . Nevertheless, most Brønsted acids-involved reactions are limited to harsh conditions (high temperature, microwave, long reaction time, and excessive acid amounts) and narrow substrate compatibility.…”

“…35 A Lewis-acid-catalyzed hydration reaction also has been reported, where the nonbenzenoid aromatic tropylium ion as an organic Lewis acid can be used to promote the hydration of alkynes. 36 Nevertheless, most Brønsted acids-involved reactions are limited to harsh conditions (high temperature, microwave, long reaction time, and excessive acid amounts) and narrow substrate compatibility.…”

Tropylium-promoted carbonyl–olefin metathesis reactions

“…Based on our previous work on the aromatic tropylium ion, 12 we envisage that tropylium could be a suitable organocatalyst for the carbonyl–olefin metathesis reaction. The concept of using an organic compound as a promoter for this type of reaction became attractive after recent developments by Lambert's group using hydrazine 2 and Franzén's group using tritylium salts.…”

CO2-Promoted Hydration of Propargylic Alcohols: Green Synthesis of α-Hydroxy Ketones by an Efficient and Recyclable AgOAc/Ionic Liquid System

“…Hydration of unsaturated bonds is one of the most straightforward and effective methodologies to produce versatile functional organic structures. − In particular, selective addition of H 2 O to acetylenic compounds has attracted tremendous attention as it provides a convenient and atom-economic route for construction of carbonyl compounds, which are considered as one of the most important structures generally existing in natural as well as industrial products. − In the past few decades, great efforts have been devoted for effective catalysis of this reaction, and a breakthrough was achieved when Kutscheroff developed the classical Hg­(II) salts/H 2 SO 4 catalytic system. , However, the high toxicity and strong corrosivity of this system blocked its further application in modern industry which pursued green and sustainable development. In recent years, a series of less toxic transition-metal catalytic systems (Cu, − Ag, − Au, − Fe, , Co, − Ru, Pd, − Pt, In, Sn and Hf,...) or metal-free systems − have been successively developed. These systems exhibited remarkable activity for most alkynes.…”