Changhui Liu

Brønsted acid ionic liquid catalyzed facile synthesis of 3-vinylindoles through direct C3 alkenylation of indoles with simple ketones

A direct dehydrative coupling protocol for the synthesis of 3-vinylindoles using easily available indoles and simple ketones as substrates was developed with the aid of a sulfonyl-containing Bronsted acid ionic liquid. The salient features of this protocol are high synthetic efficiency, a metal- and solvent-free system, a recyclable catalyst, mild conditions and easy product isolation. With the ionic liquid catalyst, a hitherto unreported straightforward method for the construction of the indolo[3,2-b]carbazole skeleton was also developed using 2-hydroxymethylindole and acetophenone as starting materials.

Brønsted Acid Ionic Liquid as a Solvent-Conserving Catalyst for Organic Reactions

A sulfonyl-containing ammonium-based Brønsted acid ionic liquid was prepared and used as a liquid heterogeneous catalyst for organic reactions. The unique macroscopic phase heterogeneity of the IL in the reaction system not only ensures an excellent catalytic activity of the IL catalyst but also avoids the use of organic reaction solvents. The catalyst system is applicable for a wide range of reactions.

Condition-determined multicomponent reactions of 1,3-dicarbonyl compounds and formaldehyde

By means of changing the reaction parameters, different products could be generated selectively starting from the same combination of substrates involving 1,3-dicarbonyl compounds and formaldehyde. This strategy enabled us to access diverse molecules without changing both starting material and reactor, maximizing thus the multifunctionality of the synthetic system. For example, starting from a 1,3-dicarbonyl compound, formaldehyde and 1,1-diphenylethylene, two kinds of products could be selectively formed including (i) a densely substituted dihydropyran and (ii) a C2-cinnamyl substituted 1,3-dicarbonyl compound. A one-pot three-component reaction of phenacylpyridinium salt, 1,3-dicarbonyl compound, and formaldehyde was also investigated, which produced either 2,4-diacyl-2,3-dihydrofuran or 2,4-diacyl-2-hydroxylmethyl-2,3-dihydrofuran in good to excellent yield.

Synergistic catalysis-induced ring-opening reactions of 2-substituted 3,4-dihydropyrans with α-oxoketene dithioacetals

According to the conventional catalytic activation mode, the difficulty of using a less reactive substrate can be alleviated by means of employing a strong catalyst. Because of the susceptibility of the reaction product to strong acid, ring-opening Friedel–Crafts reactions of 2-substituted 3,4-dihydropyrans with a less reactive nucleophile, α-oxoketene dithioacetal, could not be performed by using strong acid as a catalyst. In order to find a suitable catalyst system for this reaction, a co-catalyst, CuBr2, that can increase the reactivity of α-oxoketene dithioacetal was used in conjunction with a moderate Lewis acid, MnCl2·4H2O. The mechanism of synergistic catalysis was also studied with the aid of spectroscopic investigation. It was found for the first time that CuBr2-induced disintegration of a super-conjugation system exists in α-oxoketene dithioacetal and is responsible for the increase of its reactivity. An intramolecular Michael addition of the ring-opening product was also developed, which provided a densely substituted cyclohexane derivative in good yield. Finally, a hitherto unreported S,N-doped eleven-membered heterocycle was synthesized on the basis of the developed reactions.