关键词: 三组分反应, 二氧化碳转化, 炔丙醇, 绿色催化, 热力学有利的策略

Abstract:

Carbon dioxide (CO₂) is one of the main greenhouse gases that can be utilized as a useful C₁ source owing to its abundance, non-toxicity, and renewability. In fact, the transformation of carbon dioxide into valuable organic molecules has attracted considerable attention over the past decades. One-pot multicomponent reactions generally proceed with more than two different raw materials reacting in one pot, thus simplifying the reaction in operation and workup. In this regard, a three-component reaction of CO₂, propargylic alcohols, and nucleophiles such as amines, water, and alcohols, to prepare useful carbonyl compounds (e.g., carbamates, oxazolidinones, α-hydroxyl ketones, and organic carbonates) is particularly appealing because of the advantages of step and atom economy. From a mechanistic point of view, the three-component reaction of CO₂, a propargylic alcohol, and a nucleophile is a type of cascade reaction, involving the carboxylative cyclization of CO₂ and propargylic alcohol, and subsequent reaction of a nucleophile with the in situ formed α-alkylidene cyclic carbonate. On the other hand, reactions involving CO₂ are generally thermodynamically unfavorable because of the thermodynamic stability and kinetic inertness of CO₂. Cyclic carbonates are widely used in organic synthesis, and their preparation from vicinal diols and CO₂ represents a green synthetic method because biomass is utilized as the source of vicinal diols. However, the low yields of cyclic carbonates are obtained in most cases because of thermodynamic limitations and deactivation of the catalyst by water, which is the co-product of cyclic carbonates. The most commonly used method to improve the yields of cyclic carbonates involves the addition of dehydrating agents. However, decreased selectivity is often observed because of the side reaction of vicinal diols with the hydrolysis products of the dehydrating agent. In addition, the reaction of 2-aminoethanols and CO₂ to obtain the corresponding 2-oxazolidinones also encounters the analogous thermodynamic limitation. To solve this problem, an efficient three-component reaction of CO₂, propargylic alcohols, and nucleophiles was developed to offer thermodynamically favorable ways for converting CO₂ into cyclic carbonates and 2-oxazolidinones with vicinal diols or 2-aminoethanols as nucleophiles. In this strategy, water is not generated and the α-alkylidene cyclic carbonate formed from CO₂ and propargylic alcohol as the actual carbonyl source reacts with vicinal diol or 2-aminoethanol to give the corresponding cyclic carbonates or 2-oxazolidinones in high yields and selectivity with the simultaneous formation of hydroxyketones. This review aims to summarize and discuss the recent advances in three-component reactions of CO₂, propargylic alcohols, and nucleophiles to prepare various carbonyl compounds promoted by both metal catalysts and organocatalysts.

Key words: Three-component reaction, Carbon dioxide conversion, Propargylic alcohols, Green catalysis, Thermodynamically favorable strategy