Efficient Synthesis of Quinolines from 2-Aminoaryl Ketones with α-Methylene Carbonyl Derivatives: Exploiting the Dual Acid Sites of Metal Organic Framework Catalyst

We report on the use of heterogeneous metal organic framework (MOF) catalysts for the Friedlander synthesis of 2-aminoaryl ketone with & alpha;-methylene carbonyl derivatives, a versatile and widely used method for the synthesis of quinoline derivatives. The importance of the Lewis and Bronsted acid sites and their spatial proximity have been explored. Postsynthetic modifications were made to introduce the Bronsted -SO3H acid sites in the pristine MIL-53(Al). Two modifications were carried out, resulting in two different MOFs: MIL-53(Al)-NH-(CH2)(3)-SO3H, in which there is a significant spatial distance between the Lewis and Bronsted sites, and MIL-53(Al)-SO3H, where the two sites are in close proximity. The availability of sulfonic acid groups has a significant impact on their catalytic performance. The sulfonated MIL-53(Al) material exhibited a high yield of quinoline derivatives under solventless and mild reaction conditions, with a wide substrate scope and good reusability. Mechanistic studies revealed that the dual acidic sites of the catalysts play an important role in the reaction mechanism.