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

## TL;DR

This paper introduces new methods to improve the solubility and chemical protection of a key organic material building block using different glycols.

## Contribution

The study introduces propylene glycol and propanediol as novel protecting groups for PTO with enhanced solubility and milder deprotection.

## Key findings

- PrG-protected PTO shows 44-fold higher solubility than EtG-protected PTO.
- PD and DMPD produce 'half' protected PTOs with milder deprotection conditions.
- Protected PTOs enable functionalization reactions with high yields and chiral-optical properties.

## Abstract

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 toward bases and metal-ion chelation,
and low solubility, PTO is typically protected 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 44-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 milder
deprotection conditions for PD. All protected PTOs underwent
successful functionalization reactions with high yields. Due to its
stereocenter, use of 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.