Elemental Sulfur-Promoted Synthesis of 4-Hydroxybenzophenones from p-Quinone Methides under Metal-Free Condition

Conventional methods for the general and efficient synthesis of 4-hydroxybenzo- phenones are extremely underdeveloped and limited. We herein report a challenging metal-free protocol to rapidly construct 4-hydroxybenzophenones from para-quinone methides (p-QMs) in DMSO in the presence of KOH using the inexpensive and readily available elemental sulfur as redox reagent. As an unprecedented method, this simple but efficient approach has excellent site specificity, green sustainability, excellent atomic economy, and broad functional group compatibilities. Mechanistic studies show that the novel reaction proceeds through a radical pathway.