An electrochemical access to 2-amino-2,3-dihydro-1,4-benzodioxanes derived from hydroxytyrosol

The anodic oxidation of a natural antioxidative catechol, hydroxytyrosol, was developed in an acetonitrile/dimethylsulfoxide (or acetonitrile/water) solvent mixture to produce in a stable way the resulting non-activated o-quinone and generate structural analogues. 2-Amino-2,3-dihydro-1,4-benzodioxane derivatives were obtained as two regioisomers in good to high overall yields (65-90%) and 1 : 3 ratios, through an inverse electron demand Diels-Alder (IEDDA) reaction between the electrogenerated o-quinone and tertiary enamines. The insertion of an electron withdrawing (or electron donating) group on the catechol modified their relative proportions, so that the reaction became regiospecific. With some aliphatic enamines, a competitive 1,6-Michael addition took place, affording 2-hydroxy-1,2,4,5-tetrahydrobenzo[d]oxepine compounds.