Replacing dipolar and aprotic solvents with environmentally benign media has emerged as a new facet of green chemistry. In this paper, a sulfone‐containing imidazolium‐based Brønsted acid ionic liquid was prepared and used as a recyclable acid catalyst. The ionic liquid catalyst enables the use of an industrially acceptable and environmentally benign solvent, butyl acetate, as the reaction medium. The ionic liquid/butyl acetate biphasic system was successfully utilized in many organic reactions, which generally relied heavily on dipolar and aprotic solvents.magnified image

Dipolar and aprotic solvents are often required in acid‐catalyzed reactions, however, many of them are listed in solvent selection guides as not‐recommended due to their toxicity or explosivity. A catalytically functionalized ionic liquid, namely a sulfone‐containing imidazolium‐based Brønsted acid ionic liquid, was synthesized. It alleviates the detrimental effect of classical dipolar aprotic solvents because this ionic liquid integrates the function of a dipolar aprotic solvent able to stabilize carbocation intermediates and the activating effect of a strong Brønsted acid on electrophiles. The use of this tailor‐made ionic liquid was exemplified in some transformation reactions of indoles, which proceeded with high yield and selectivity using a green and an industrially acceptable solvent, butyl acetate. The recyclability of the ionic liquid catalyst was also demonstrated.

Benzo[a]carbazoles were synthesized from 2-phenylindoles and a-bromoacetaldehyde using bismuth trichloride as a catalyst. The reaction was triggered by a bismuth trichloride-catalyzed Friedel-Crafts alkylation of these two precursors, which provided a tryptaldehyde intermediate that underwent intramolecular olefination to form the final product. Interestingly, the HBr byproduct generated in the upstream step of the reaction catalyzed the following downstream reaction steps, thus creating a byproduct-participated relay catalytic process. Motivated by this mechanism, we developed a three-component reaction of indole, abromoacetaldehyde acetal, and 1,3-dicarbonyl compounds. This study offers a straightforward method for synthesizing substituted carbazoles.

No abstract

No abstract