One-pot Three-component Synthesis of Fully and Diversely Functionalized Pyrans and Spiropyrans using Sodium Formate as Catalyst in Aqueous Ethanol at Room Temperature

A convenient and general method has been developed for the synthesis of fully and diversely functionalized pyrans via one-pot three-component reactions of various aryl or heteroaryl aldehydes, malononitrile, and 1,3-dimethyl/1,3-diethyl-acetonedicarboxylates in the presence of a catalytic amount of sodium formate as an efficient organocatalyst in aqueous ethanol at room temperature. All the scaffolds were synthesized in excellent yields within 2.5 hours. Under the same reaction conditions, fully and diversely functionalized spiro-pyrans were also synthesized in excellent yields from the reaction of isatin, malononitrile, and 1,3-dimethyl/1,3-diethylacetonedicarboxylates. All the products were isolated pure just by simple filtration. Synthesis of fully and diversely functionalized biologically promising pyrans, excellent yields, use of organocatalyst, less toxic solvent, no column chromatographic purification, and energy efficiency are some of the major advantages of this newly developed protocol.