Scheme 17. Schreiber's exploitation of the Ugi and Diels–Alder reactions and metathesis chemistry in combination. Reagents and conditions: (1) MeOH–THF, (2 : 1), 60 h; (2) KHMDS, allyl bromide; (3) Grubbs' 2nd-gen. cat., CH₂Cl₂, 40 °C, 60 h; (4) HF·pyridine, CH₂Cl₂, 2 h. Ar = m-bromophenyl.