20017-39-4Relevant articles and documents
Elemental Sulfur-Promoted Synthesis of 4-Hydroxybenzophenones from p-Quinone Methides under Metal-Free Condition
Li, Jingping,Wang, Kunpeng,Wu, Jiayi,Zhang, Haoxiang,Chen, Yan,Liu, Qinglei,Xu, Junju,Yi, Weiyin
, (2022/05/20)
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.
Chemistry of photogenerated α-phenyl-substituted o-, m-, and p-quinone methides from phenol derivatives in aqueous solution
Diao, Li,Wan, Peter
, p. 105 - 118 (2008/09/18)
The enhanced photochemical reactivity of o-substituted phenols in its propensity to give o-quinone methide (o-QM) intermediates via excited state intramolecular proton transfer (ESIPT) was uncovered by Keith Yates as part of his now classic studies of photohydration of aromatic alkenes, alkynes, and related compounds. Photogeneration of QMs and the study of their chemistry along with potential biological applications are the focus of many groups. In this work, photochemical precursors to o-, m-, and p-QMs based on substituted phenols (hydroxybenzyl alcohols) and related compounds have been studied in aqueous solution as a function of pH and water content. The focus will be on QMs that are stabilized by an a-phenyl substituent, which enhances quantum yields for their formation, with the resulting QMs having longer lifetimes and easier to detect. Noteworthy is that all QM isomers can. be photogenerated with the o and m isomers being the most efficient, consistent with the Zimmerman "ortho-meta" effect. m-QMs have formal non-Kekule structures, and although they can be routinely photogenerated, are found to be most reactive. One m-QM was found, to undergo a photocondensation reaction at high pH giving rise to m-substituted oligomers. The mechanism, of QM formation in aqueous solution is believed to involve singlet excited phenols that undergo adiabatic deprotonation to give the corresponding photoexcited phenolate ion, which subsequently expels the hydroxide ion (photodehydroxylation). A pathway involving direct loss of water for the o-isomers is also possible in organic solvents.
