Studies of Stereo-selective Cyclo-additions and Transformations of Substituted 2-cyclopenten-1-one with Chiral Anthracene templates

The chiral (S)-9-(1-methoxyethyl), (R)-9-(1,2-dimethoxyethyl) and 9-(1R, 2R)-(1,2-dimethoxypropyl) anthracenes were synthesised and used for the thermal Diels-Alder reaction with cyclopentene-3,5-dione. Unlike the maleic anhydride and N-substituted malemides, the cyclo-adducts were obtained with high regio-selectivity as a single diastereomer. The X-ray structure of the cyclo-adduct showed an enol form but the ¹³C NMR showed resonances for two cyclopentanone carbonyl groups suggesting the solution structure is in the diketone form. Stereo-controlled studies using organomagnesium additions to the carbonyl groups resulted in hydrolytic cleavage of the enol ether and elimination of water to give â-alkylketone anthracene adducts. These were unsuccessful in preparing chiral cyclopentenone core structures.