Used attributively with reference to a synthetic method involving the addition of a conjugated diene to a compound with a double or triple bond so as to form a six-membered ring; especially in "Diels–Alder reaction." Compare "diene synthesis".
1930s; earliest use found in Journal of the Chemical Society. From the names of Otto Diels and Kurt Alder, German chemists, who described such reactions in a series of papers beginning in 1928 (Ann. der Chem 460 98–122).