Heteropoly acid-catalyzed three-component aza-Diels–Alder reaction in a continuous micro-flow system

Abstract

The first direct aza-Diels-Alder reaction catalyzed by phosphotungstic acid combined with a water absorption device in the micro-flow system was reported. The optimization process gave the azabicyclo [2.2.2] octan-5-ones in 98.78% conversion and an endo/exo ratio of 7/93. Exo cycloadducts were quickly prepared due to the efficient mixing and heat transfer in the micro-flow system. However, exo products could be turned into endo cycloadducts which were more stable.

Tandem, Effective Continuous Flow Process for the Epoxidation of Cyclohexene

“…Next, we sought to use the m-CPBA generated in the previous peroxidatic reaction for further epoxidation under flow conditions. In light of previous research reported by our group, , the HCOOH/H 2 O 2 system in the MFS was an efficient approach to prepare peroxides. However, no cyclohexene oxide was observed in the preliminary experiment.…”

“…Following the inspiring contributions by Jensen et al and Hessel et al, , various applications of MFS appeared in the literature in the recent years. − The excellent mass and heat transfer can be achieved by virtue of enhanced surface-to-volume ratio. With the aid of precise temperature and efficient mixing control, the reaction can be completed within a shorter time to obtain better yields and excellent diastereoselectivity . In the previous study, epoxidation of soybean oil and fatty acid methyl esters combined with continuous separation were investigated .…”

Tritylium Cation as Low Loading Lewis Acidic Organocatalyst in Povarov Reactions

“…To circumvent this obstacle, we adopted a two-stage, threecomponent Povarov reaction through a continuous flow layout with a water absorption device (Scheme 4b). 46,47 As shown in Scheme 4b, a benzaldehyde solution and aniline solution were pumped into the microreactor I, then the resulting imine solution and 2,3-dihydrofuran solution containing tritylium tetrafluoroborate were pumped into the same microreactor II.…”

“…The yields were always somewhat lower, however, which may be attributed to the decomposition or deactivation of the carbenium by water formed during imine formation. To circumvent this obstacle, we adopted a two-stage, three-component Povarov reaction through a continuous flow layout with a water absorption device (Scheme b). , As shown in Scheme b, a benzaldehyde solution and aniline solution were pumped into the microreactor I, then the resulting imine solution and 2,3-dihydrofuran solution containing tritylium tetrafluoroborate were pumped into the same microreactor II. To our delight, 89% yield was obtained at a residence time of 2 min at a total flow rate of 5 mL/min (Figure S57 in the Supporting Information).…”

A comprehensive review of flow chemistry techniques tailored to the flavours and fragrances industries

“…Alternative methods of catalysis have also been developed over the past few decades which offer feasible transposition to flow. Zeolite [ 432 – 433 ], heteropoly acids (HPA) [ 434 ] and other Lewis acid catalysis [ 435 ] have been exploited under flow conditions.…”