Generation of heterocyclic quinone methides from ortho-hydroxy methyl derivatives and a study of their cycloaddition reactions

Quinolinone quinone methide (1a), prepared from 1,3-dimethyl-4-hydroxyquinolin-2-one and 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), gives a dimer (5) and reacts in situ with 2,2-dimethyl-2H-1-benzopyran, and with isopropenyl acetate, to give Diels–Alder cycloaddition products; coumarin quinone methides behave similarly with 2,2-dimethylbenzopyran, but with isopropenyl acetate and with 2,3-benzofuran give adducts that probably result from [2 + 2] cycloaddition reactions.