Fast, easy, solvent-free, microwave-promoted Michael addition of anilines to α,β-unsaturated alkenes: synthesis of N-aryl functionalized β-amino esters and acids

Starting With Microwave Chemistry

“…In general, when employing parallel rotors in multimode instruments, temperature monitoring is provided via a fiberoptic probe in one reference vessel and an external IR sensor that records the temperatures for all the rotor vessels. In particular, when low microwave absorbing solvents (or no solvent at all) are used in a library synthesis, the heating characteristics of the individual reaction mixtures are strongly dependent on the microwave absorptivity of the specific building blocks, thus leading to different temperatures in the reaction vessels, resulting in different conversions compared to a single-mode sequential method [11]. In such a case, the positioning of the fiber-optic sensor is crucial since the vessel with the fiber-optic probe is used as the control.…”

Microwave Processing Techniques

“…Investigations of this phenomenon have been conducted by Leadbeater in a combined multi-and single-mode instrument (Milestone Multi-SYNTH, Figure 3.30) [98]. For example, decomposition of the reaction involving m-anisidine 37 was observed that indicated a temperature higher than 200 C, whereas for N-ethylaniline 38 a lower conversion was obtained corresponding to a temperature lower than 200 C (Scheme 4.25) [99]. A case in point is the Michael addition of anilines with methyl acrylate, which is best performed under neat conditions at 200 C, as demonstrated by a single-mode experiment (Scheme 4.25) [99].…”

“…In particular, when low microwave-absorbing solvents are used (or no solvent at all), the heating characteristics of the reaction mixture are strongly dependent on the microwave absorptivity of the building blocks, thus leading to different temperatures in the reaction vessels, and different conversions compared to a single-mode sequential method can arise. These effects could be minimized either by using a high absorbing solvent or by adding polar additives such as TBAB [99]. Since this reaction is highly temperature dependent, lower temperatures in general give poorer yields whereas higher temperatures may lead to side-product formation and decomposition.…”

Microwave Assisted Heterofunctionalization of Alkenes and Alkynes

“…Leadbeater recently reported the formation of functionalized amines via the acetic acid catalyzed addition of primary aryl amines to acrylates (eqn 3), vinyl sulfones, and acrylonitrile using focused and multimode microwave reactors [29,30]. The addition reactions selectively generated the 1,4-addition product in high yields after 20 minutes (200 °C using an external IR sensor) of irradiation.…”