Scheme 3. Synthetic utility of the tetracyclic skeleton of waihoensene. Reagents and conditions: (a) pyrrolidine, Et₃N, neat, 85 °C, then TBDPSCl, imidazole, CH₂Cl₂, 0 °C (98%); (b) Tf₂O, 2,6-di-tert-butyl-4-methylpyridine, DCE, reflux, then CCl₄/H₂O reflux (54%); (c) 2-bromopropene, t-BuLi, THF, −78 °C (85% brsm); (d) TESOTf, 2,6-lutidine, CH₂Cl₂, 0 °C (94%); (e) SeO₂, TBHP, CH₂Cl₂, 0 °C – rt (73% brsm); (f) CBr₄, PPh₃, imidazole, CH₂Cl₂, rt (90%); (g) prop-2-yn-1-yl acetate, CuOAc, Cs₂CO₃, DCE, 70 °C, then AuCl₃, PTS, HFB (hexafluorobenzene), rt (40%, dr = 3.2 : 1); (h) TBAF, THF, 0 °C (93%); (i) IBX, EtOAc, reflux (91%); (j) K₂CO₃, MeOH/H₂O = 100 : 1, 0 °C – rt (64%); (k) HCl, THF, rt (89%). TBDPSCl = tert-butyl diphenylchlorosilane, DCE = 1,2-dichloroethane, TESOTf = triethylsilyl trifluoromethanesulphonate, IBX = 2-iodoxybenzoic acid.