Cycloaddition reactions of o-quinone methides with polarized olefins

The review summarizes and systematizes the [4+2]-cycloaddition reactions of o-quinone methides with electron-rich and electron-deficient olefins. The electron-rich substrates include vinyl ethers, vinyl sulfides, enamines, enamides, enols, furans, benzofurans and indoles, while the electron-deficient substrates are esters of unsaturated carboxylic acids, vinyl azides and quinones. Reactions with push-pull and captodative olefins are also considered. The mechanisms of some reactions are presented. A separate part of the review addresses reactions of p-quinone methides containing an o-hydroxyphenyl substituent at the exocyclic carbon atom, which can isomerize to o-quinone methides. Much attention is paid to oligomerization of o-quinone methides, which proceeds in the absence of active dienophiles or nucleophiles. The bibliography includes 217 references.