Glycerol as a biodegradable and reusable promoting medium for the catalyst-free one-pot three component synthesis of 4H-pyrans

Glycerol is applied as a green, biodegradable and reusable promoting medium for one-pot three component synthesis of 4H-pyrans under catalyst-free conditions. A broad range of substrates including aromatic and heteroaromatic aldehydes, isatine derivatives, acenaphthenequinone and ninehydrine are condensed with carbonyl compounds possessing a reactive α-methylene group and alkylmalonates. All reactions are completed in short times, and the products are obtained in good to excellent yields. The reaction medium could be recycled and reused several times without any loss of efficiency.