Scheme 25. Martin's branching pathway for heterocycle synthesis following a multicomponent reaction. Reagents and conditions: (1) propargyl amine, AcCl, allylZnBr, CH2Cl2, 63%; (2) allyl amine, BnCOCl, allylZnBr 4 Å MS, THF, 91%; (3) allylN(TMS)2, 10% TMSOTf, CH2Cl2 then CH2CHOTBS, AcCl, 78%; (4) MeNH2, 95, THF, Δ, then 94, –78 °C, 61%; (5) Hoveyda–Grubbs' 2nd-gen. cat., CH2Cl2, styrene, then NaHMDS, 55%; (6) Grubbs' 2nd-gen. cat., CH2Cl2, then Pd[P(tBu)3]2, DIPEA, Bu4NCl, MeCN, MW, 120 °C, 65%; (7) MeNHOH·HCl, Et3N, PhMe, Δ, 87%; (8) conc. HCl–MeOH (2 : 1), 71%.
