1995 MERCK-FROSST-AWARD-LECTURE - QUINONE METHIDES - RELEVANT INTERMEDIATES IN ORGANIC-CHEMISTRY

ortho and para-Quinone methides (2-methylene-3,5-cyclohexadien-1-one a nd 4-methylene-2,5-cyclohexadien-1 one, respectively) are intermediate s in a variety of important chemical systems. In particular, o-quinone methides are useful in synthesis for the construction of chroman ring systems. A brief account of the relevance of quinone methide chemistr y will be provided. This is followed by a review of recent studies fro m our laboratory on efficient methods for the photogeneration of quino ne methides, concentrating on the use of hydroxy-substituted benzyl al cohols in aqueous media. It is shown that this method is general since it provides access to o-, m-, and p-quinone methide isomers. When app ropriately substituted, all of these quinone methide isomers have been spectroscopically characterized by laser flash photolysis, making thi s technique the one of choice for studying the dynamics of these react ive intermediates. The mechanism of photochemical generation from hydr oxybenzyl alcohols and extensions of the reaction to photogeneration o f fluorenyl and biphenyl quinone methides will also be presented.