Electrocatalytic Cascade Reaction of Aldehydes and 4-Hydroxy-6-methyl-2 H -pyran-2-one

The electrolysis of salicylaldehydes and 4-hydroxy-6-methyl-2H-pyran-2-one in an undivided cell in alcoholic media and in the presence of alkali metal halides results in rapid and efficient formation of the substituted 3-acetoacetylcoumarins in 85–93% product yields and 425–930% current efficiency. This novel chain electrocatalytic process reveals a “green” and advantageous route to functionalized 3-acetoacetylcoumarins having promising properties for the different biomedical and other practical applications. The analogous process with arylaldehydes leads to substituted 3,3′-(arylmethylene)bis(4-hydroxy-6-methyl-2H-pyran-2-ones). Thus, under mild conditions, this simple electrocatalytic system produces the electrochemically induced Knoevenagel condensation of aldehydes and 6-methyl-2H-pyran-2-one with either subsequent rearrangement in case of salicylaldehydes towards 3-acetoacetylcoumarins or further addition of 6-methyl-2H-pyran-2-one molecule in case of arylaldehydes, leading to substituted 3,3′-(arylmethylene)bis(4-hydroxy-6-methyl-2H-pyran-2-ones).