Diels–Alder: a concerted [4+2] cycloaddition
A 4π diene and a 2π dienophile reorganise six electrons through one cyclic transition state — no intermediates, stereospecific, and usually giving the endo adduct.
A 4π diene and a 2π dienophile reorganise six electrons through one cyclic transition state — no intermediates, stereospecific, and usually giving the endo adduct.