Enhanced Solubility and Deprotection of Pyrene-4,5,9,10-tetraones through Propylene Glycol and Propane Diol Protection

Pyrene-4,5,9,10-tetraone (PTO) is a building block of significant interest for functional organic materials. Due to the sensitivity of the vicinal diones towards bases or metal ion chelation, and to improve solubility, PTO is typically pro-tected as a ketal with ethylene glycol (EtG). Herein, we report the use of propylene glycol (PrG), propane-1,3-diol (PD)- or 2,2-dimethylpropane-1,3-diol (DMPD) for its protection. The PrG-protected PTO has a 49-fold increased solubility relative to EtG-protected PTO due the introduced regio- and stereoisomerism. Protection with PD and DMPD surprisingly produced “half”-protected PTOs with maintained protective capabilities, and deprotection under milder conditions for PD. The new series of protected PTOs all underwent successful functionalization reactions with high yields. Due to its stereocenter, use of the PrG-protecting groups gives entry to protected PTOs with chiral-optical properties. This new series of ketal-protecting groups should considerably facilitate the future synthesis of PTO-based materials.