Design and synthetic efforts toward a chiral anthraquinone

This dissertation reports on the synthetic efforts towards (S)-1,6-dihydroxy-7-(1-hydroxyethyl)anthracene-9,10-dione (3), an anthraquinone which is analogous to a naturally occurring (S)-1,2,6-trihydroxy-7-(1- hydroxyethyl) anthracene-9,10-dione (4), from simple and readily available anacardic acid (5). The main goal was to prepare the substituted phthalic anhydride namely 4-methoxyisobenzofuran-1,3-dione (6) from anacardic acid (5) and subsequently couple this phthalic anhydride with the benzene derivative (s)-2-(1- hydroxyethyl)phenol (7) to obtain the targeted anthraquinone 3. Anacardic acid, the major phenolic constituent of natural cashew nut shell liquid was isolated as a stable salt of calcium and used as starting material in the synthesis. Subjecting this through a series of reactions gave the desired 3-methoxyphthalic anhydride 6. The benzene derivative, 2-acetylphenol (8), which is the immediate synthetic precursor of 7, was prepared from phenol. Subsequently, Friedel-Crafts Acylation (FCA) was employed in coupling 6 and 8 to get anthraquinone 7-acetyl-1,6dihydroxyanthracene-9,10-dione (50), which is very advanced precursor of targeted anthraquinone 3. However, the face reaction gave the anthraquinone 2-acetyl-1,8-dihydroxyanthracene-9,10-dione (51) which was obtained in small quantity and moderate purity and thus hindered its complete structural assignment as well as its further information. During the synthesis, the progress of the reaction was monitored by TLC whereas column chromatography was used in the purification of most of the synthesized compounds. Both 1H- and 13C-NMR techniques were used in the confirmation of the chemical structure of the synthesized compounds.