Quinone methide generation

Both o- and p- substituted bis(methylthio)arylmethylium salts, derived by the 5-methylation of substituted dithiobenzoates, dimerise following deprotonation to give 1,4-dithianes. Only with the former isomer is the quinone methide generated leading to a cyclooctene derivative <96LA1159>. 

A third reaction pathway for quinone methides generated following ESIPT to aromatic carbon (in addition to H-D exchange and cyclization) was observed following the examination of the photochemistry of 9-(2 -hydroxyphenyl)anthracene... 

Zeng, Q. Rokita, S. E. Tandem quinone methide generation for cross-linking DNA. J. Org. Chem. 1996, 61, 9080-9081. 

Several general synthetic methods have been developed that utilize the novel reactivity of quinone methides generated by oxidation of phenol precursors. Angle and Ranier have generated 2,6-dialkyl or 2,6-dialkoxy-substituted / -quinone methides 51 by oxidation of the corresponding phenols with Ag20. 

STEVEN E. ROKITA, PhD, is Professor in the Department of Chemistry and Biochemistry at the University of Maryland. His research interests lie in sequence and conformation specihc reachons of nucleic acids, enzyme-mediated activation of substrates and coenzymes, halogenation and dehalogenation reactions in biology, and aromatic substitution and quinone methide generation in bioorganic chemistry. 

Since the remarkable demonstration of the facility of an intramolecular Diels-Alder reaction (dimerization) of an o-quinone methide, generated by the oxidation of a substituted o-alkylphenol in the development of a biomimetic synthesis of carpanone [Eq. (44)],170... 

Full details of a careful study of the regio- and stereospecific intramolecular [4 + 2] cycloadditions of o-quinone methides generated by the thermal or acid-catalyzed (CF3CO2H) dehydration of o-hydroxybenzyl alcohols have been described 75 and have found application in the total synthesis of enantiomerically pure (3/ )-26 and (3/ )-27 possessing the ring system and correct absolute configuration of the cannabinol family [Eq. (47)]. 

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