Antimony pentachloride catalyzed Diels–Alder reactions: improved regioselectivity in the synthesis of dialkyl naphthoquinones

Improved regioselectivity in catalyzed Diels–Alder (DA) cycloadditions between non-symmetrical benzoquinones and mono-substituted butadienes is achieved by use of SbCl5. After oxidation, good yields of dialkylnaphthoquinones are obtained. The greater steric demand in comparison to other Lewis acids (LAs) seems to favor the less hindered transition state.