Superheated dichloromethane

Diels-Alder cycloaddition of 5-bromo-2-pyrone with the electron-rich tert-butyldi-methylsilyl (TBS) enol ether of acetaldehyde, using superheated dichloromethane as solvent, has been investigated by Joullie and coworkers (Scheme 6.90) [188]. While the reaction in a sealed tube at 95 °C required 5 days to reach completion, the anticipated oxabicyclo[2.2.2]octenone core was obtained within 6 h by microwave irradiation at 100 °C. The endo adduct was obtained as the main product. Similar results and selectivities were also obtained with a more elaborate bis-olefin, although the desired product was obtained in diminished yield. Related cydoaddition reactions involving 2-pyrones have been discussed in Section 2.5.3 (see Scheme 2.4) [189]. 

Baumann et al. [6] also utilized a commercially available flow reactor. The setup from Vapourtec (www.vapourtec.co.uk) exhibits HPLC pumps, sample loops containing a maximum of 2 ml substrate solution each, and the so-called convection flow coil (ID 1 mm, V=9ml) as residence time module (Figure 6.8). The procedure was similar to that of Seeberger et al. with superheated dichloromethane as solvent, the reactions were carried out at temperatures of 70-90 °C and 100 psi (6.9 bar). With an overall flow rate of 0.3 ml/min... 

In 2008, important developments on the fluorination with DAST on laboratory scale were presented by Gustafsson et cd. [5]. The authors utilized a commercially available microfluidic Syrris FRX system (www.syrris.com) with HPLC pumps and PTFE tubings with an ID of 1 mm (V= 16ml) for the development of a DAST deoxofluorination protocol for a variety of substrates, for example, alcohols, lactols, aldehydes, and carboxylic adds (Figures 6.6 and 6.7). One of the main features of the protocol is the short residence time of 16 min. The reactions were run in dichloromethane and superheating to 70 °C under a pressure of 75psi (5.1 bar) allowed for shortened reaction time. As described... 

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