Microwave irradiation clay-adsorbed reactions

Loupy and colleagues have prepared acetals of 1-galactono-l,4-lactone in excellent yields [31] by adsorbing the lactone and the aldehyde on montmorillonite K 10 or KSF clay followed by exposing the reaction mixture to microwave irradiation (Scheme 6.1). 

Montmorillonite K-10 clay (1.0 g) is mixed with la (0.1 g, 0.45 mmol) in solid state using a pestle and mortar or alternatively with a solution of la in dichloro-methane (2 mL). The adsorbed material is transferred to a glass tube and is inserted in an alumina bath (alumnia 100 g, mesh 65-325, Fisher scientific bath 5.7 cm diameter) inside the microwave oven. The compound is irradiated for 1.5 min (the temperature of alumina bath reached 110°C at the end of this period) and the completion of the reaction is monitored by TLC examination. The product is extracted into dichloromethane (2x15 mL) and clay is filtered off. Removal of the solvent under reduced pressure affords 2-phenyl-1,2,3,4-tetraliydro-4-quinolone 2a, in 80% yield, mp 148-150 °C. 

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