Studying the Morita-Baylis-Hillman Reaction in Continuous Flow Using Packed Bed Reactors

PDI-Functionalized Glass Beads: Efficient, Metal-Free Heterogeneous Photocatalysts Suitable for Flow Photochemistry

Perylene diimides (PDI) have an extraordinary ability to activate both energy and electron transfer processes upon light excitation; however, their extremely low solubility has hindered their wide use as photocatalysts. Here, we show that the combination of solid-supported PDIs with continuous flow photochemistry offers a promising strategy for process intensification and a scalable platform for heterogeneous photocatalysis. The photocatalyst immobilized onto glass beads is highly efficient, easy to separate, and extremely reusable, with a broad synthetic application range. Using the photo-oxidation of n-butyl sulfide as a benchmark reaction, we demonstrate that immobilized PDI are highly active, outperforming reported homogeneous photosensitizers, and capable of extensive reuse (turnover number (TON) >57,000 over 2 months). Transferring the process from batch to flow results in a 10-fold reduction in irradiation time and an increase in the space-time yield by a factor of 33 (40 vs 1338 mmol-1 h-1 L-1 batch vs flow). What is more, the same catalyst sample can be used for the preparation of a range of sulfoxides, the aza-Henry reaction between nitromethane and N-Ar tetrahydroisoquinolines, and the photo-oxidation of furfural with high catalytic activity. Overall, our work combines the remarkable photocatalytic properties of PDI with inert, easy-to-handle glass beads, producing hybrid materials that are reusable and can be adapted for performing heterogeneous photocatalysis in a range of scalable photochemical reactors.

Acceleration of Baylis-Hillman Reaction using Ionic Liquid Supported Organocatalyst

Background:

Baylis-Hillman reaction requires cheap starting materials, easy reaction protocol, and possibility to create the chiral center in the reaction product has increased the synthetic efficacy of this reaction which also suffers from high catalyst loading, low reaction rate, and poor yield.

Objective:

The extensive use of various functional or non-functional ionic liquids (ILs) with organocatalyst acts not only as reaction medium but also as a support to anchor the catalysts to increase the reaction rate of various organic transformations.

Methods:

In this manuscript, we have demonstrated the synthesis of quinuclidine-supported trimethylamine-based functionalized ionic liquid as a catalyst for the Baylis-Hillman reaction.

Results:

We obtained the Baylis-Hillman adducts in good, isolated yield along with low catalyst loading, short reaction time, wide substrate scope, easy product, and catalyst recycling. N- ((E,3S,4R)-5-benzylidene-tetrahydro-4-hydroxy-6-oxo-2H-pyran-3-yl) palmitamide was also successfully synthesized using CATALYST-3 promoted Baylis-Hillman reaction.

Conclusion:

We successfully isolated the 25 types of Baylis-Hillman adducts using three different quinuclidine-supported ammonium-based ionic liquids such as Et3AmQ][BF4] (CATALYST-1), [Et3AmQ][PF6] (CATALYST-2), and [TMAAmEQ][NTf2](CATALYST-3) as new and efficient catalysts. Generally, all the reactions demonstrated higher activity and gave good to high yield in competition with various previously reported homogenous and heterogeneous catalytic systems. Easy catalyst and product recovery followed by 6 times of catalysts recycling were the added advantages of the prosed catalytic system. Tedious and highly active N-((E,3S,4R)-5-benzylidene-tetrahydro- 4-hydroxy-6-oxo-2H-pyran-3-yl) palmitamide derivative was also synthesized using CATALYST- 3 followed by Baylis-Hillman reaction.