Four-Component Synthesis of 3,4-Dihydro-coumarin Derivatives

Significance

Reported is the synthesis of substituted 3,4-dihydrocoumarin derivatives by a four-component condensation reaction of salicylaldehydes, Meldrum’s acid, alkyl or aryl isocyanides, and aromatic or aliphatic alcohols. The authors propose initial formation of conjugated electron-deficient heterodiene by standard Knoevenagel condensation of 2-hydroxybenzaldehydes and Meldrum’s acid, followed by a [4+1] cycloaddition or a Michael-type addition with isocyanide to afford an iminolactone intermediate. Then, nucleophilic attack of the R^²OH component to the activated carbonyl moiety of the intermediate yields the product.