The Diels-Alder reactions of 6-hydroxy-, 6-methoxy-, and 6-acetoxynaphthoquinone with trans-l-methoxy-3-methyl-1, 3-butadiene have been studied, and the regiochemistry of the adducts has been determined. The results are consistent with the hypothesis that the acetoxy (as well as the hydroxy and methoxy) substituent functions as an electron donor despite Hammett u constants which would suggest otherwise.
