Sequential MW irradiation

Three reactions of 1 successively with diethyl fumarate, maleic anhydride, and dimethyl acetylenedicarboxylate (DMAD) are highly representative of the variety of experimental conditions used in the GS/MW process [26, 27]. Continuous MW irradiation (CMWI) with an incident power of 120 W for 1 min led to a high increase in temperature (Tmax> 300 °C). Adduct 4 was obtained almost quantitatively (Tab. 7.1, entry 1), whereas only traces of adducts 5 and 6 were detected. When the incident power was reduced (30 W) and sequential MW irradiation (SMWI) was used, adducts 5 and 6 were obtained in good yield (Tab. 7.1, entries 3 and 4). This controlled irradiation enabled the temperature to be limited (Tmax < 200 °C) and avoided the retro-DA reaction. In the reaction between 1 and diethyl fumarate similar SMWI conditions also gave the adduct 4 in high yield (Tab. 7.1, entry 2). 

Sequential MW irradiation (SMWI) applied incident power time and number of irradiations interval between two irradiations 2 min (entries 2-5), 1 min (entries 6-9) e Not given f This work... 

Mass of 70 2.19 g (15 mmol) mass of graphite 5 g b Sequential MW irradiation controlled to a maximum temperature of 450 °C c Applied incident power and irradiation time interval between two irradiations 2 min d Yield of cyclopentanone (74) from GC analysis... 

In 2000, Dubac s group reported the microwave-assisted Friedel-Crafts acylation of slightly activated and deactivated arenes under solvent-free conditions with FeCl3 as catalyst. Here, for the acylation of toluene a 90% product yield is obtained after 5 min of irradiation and an overall reaction time of 30 min in the presence of only 5 mol% of FeCl3. A sequential MW irradiation at 300 W afforded the acylation of fluorobenzene with 2 -chlorobenzoyl chloride, with a surprisingly high yield of 92% of 2-chloro-4 -fluorobenzophenone (Scheme 6.11). 

The hetero-DA reaction with azadienes, a well known synthetic method for obtaining nitrogen heterocycles, suffers from some difficulties, because of the low reactivity of the diene. For example, azadiene 2 did not react with DMAD under the action of conventional heating [22], Sequential exposure to MW irradiation (30 W) for 10 min on a graphite support (Tmax = 171 °C) led to the adduct 7 with 60% conversion (50% in isolated product) [26, 27]. An equivalent yield was obtained by ultrasonic irradiation of the neat reaction mixture at 50 °C for 50 h [29]. 

Fig. 9 TEM images and D/G Raman bands for (a) pristine MWCNT, (b) after MW irradiation (2.45 GHz), (c) after sequential MW-US (20 kHz) irradiation, (d) sonication at 20 kHz, and (e) sonication at 300 kHz. Reproduced with permission from [69]. Copyright 2011 The Royal Society of Chemistry...

Figure 16 CD spectra of a thin film (340 nm) of 41 on glass, as prepared (full line) and after sequential irradiation of l-CPL (dashed line) and r-CPL (dotted line) at 488 nm (7—160 mW cm 2). (Reproduced from Ref. 99 2002, Wiley-VCH.)...

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