The reaction of 4-hydroxycoumarins with 2-dimethylaminoethyl ketones or with dimethylamine + vinyl ketones affords 4-hydroxy-2-oxo-3-(3-oxoalkyl)-2H-1-benzopyrans which undergo carbonyl olefination with methylenetriphenylphosphorane to give 3-(3-butenyl)-4-hydroxy-2-oxo-2H-1-benzopyrans [3-(3-butenyl)-4-hydroxycoumarins].