Mechanistic investigations in diastereoselective Diels-Alder additions of chiral 9-anthrylethanol derivatives

The preparation and subsequent Diels-Alder addition reactions of chiral 9-functionalised anthracene derivatives have been investigated. 9-(1-Methoxyethyl) anthracene undergoes highly diastereoselective (> 95 : 5) thermal and photoinduced Diels-Alder additions with maleic anhydride and N-methylmaleimide. The corresponding reactions of 1-anthracen-9-ylethanol occur with the reverse sense of selectivity for additions with maleic anhydride with a corresponding increase in the reaction rate. The origins of this selectivity have been proposed to lie in hydrogen-bonding effects. The stereochemical outcome of the Diels-Alder additions has been determined from single X-ray crystallography of adducts 5 and 7. Solvent effects on the diastereoselectivity of these reactions have also been observed.