Diels–Alder cycloadditions by microwave-assisted, continuous flow organic synthesis (MACOS): the role of metal films in the flow tube

Abstract

Thin Pd films have been deposited on the inside of capillary-sized tubes through which compounds undergoing Diels-Alder reactions have been flowed while being heated with microwave irradiation; dramatic rate accelerations are observed in the presence of the film, which has been shown to play both a heating and catalytic role.

Microwave‐Assisted Continuous Flow Organic Synthesis (MACOS)

“…This methodology was then applied to the nucleophilic substitution (S N Ar) of aromatic fluorides (82) with primary amines (83) that produced the anilines (84). The presence of the Pd film inside of capillary tubes has both a heating and a catalytic role in Diels-Alder cycloadditions [73]. This observation was proved in different cycloadditions between several dienes with dienophiles flowing through the microwave reactor previously described.…”

“…Organ and co-workers used a different alternative. They coated thin metal films on the inner surface of capillaries as immobilized nanometer-sized catalysts and also microwave antenna [70][71][72][73][74][75][76][77]. The continuous flow reactor (Figure 25.15) consisted of a stainless-steel holding/mixing chamber with three or four inlet ports that merge into one or two outlets.…”

Accessing Stereochemically Rich Sultams via Microwave-assisted, Continuous-flow Organic Synthesis (MACOS) Scale-out

“…viii To address these limitations, the MACOS platform was employed to scale-out, rather than scale-up, the scaffold production runs. ix,x The scale-out approach to microwave transformations has been shown in recent years to be a highly efficient method for accessing large quantities of organic molecules. xi,xii …”

Continuous‐flow syntheses of heterocycles

“…A custom-built microcapillary reactor was used by Shore and Organ [17] for performing a Diels-Alder cycloaddition reaction under microwave flow conditions. A thin Pd film on the inner surface of inexpensive glass capillaries was used, displaying excellent heating behavior under microwave irradiation conditions.…”