Systematic Study of a Solvent-Free Mechanochemically Induced Domino Oxa-Michael-Aldol Reaction in a Ball Mill

Abstract

A systematical investigation of the parameters influencing on mechanical processing, ball milling, of organic reactants has been carried out. As model reactions, domino oxa-Michael-aldol reactions yielding tetrahydroxanthenones have been chosen.

Key words

solvent-free - ball mill - domino oxa-Michael-aldol reaction - tetrahydroxanthenone - dihydrobenzopyran

References and Notes

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11

All reactions were performed in a Ball Mill PM 100 Retsch with a fixed transmission ratio (1:2). In a typical experiment, salicylaldehyde (1 equiv), cyclohexenone (1 or 2 equiv), and DABCO (0.5 equiv) were ball milled over periods of 30 min with five-minute breaks between each. Afterwards, the vessel and the balls were rigorously washed with EtOAc. The combined organic phases were washed three times with H₂O, dried over Na₂SO₄, filtered off, and reduced under vacuum. The residue was purified via silica gel column chromatography.