Figure 3: Access to the core structure for both arcutane diterpenes and arcutine alkaloids.

(a) Conditions: (a) Ph₃PCH₂OMeCl, t-BuOK, THF, 0 °C; then TMSCl, NaI, MeCN, −18 °C; (b) NaBH₄, MeOH, 0 °C, 55% over two steps; (c) acryloyl chloride, Et₃N, CH₂Cl₂, rt; (d) TBAF, THF, rt, 77% over two steps; (e) PIDA, MeOH, 0 °C; then xylene, BHT, 150 °C; 72%; (f) SmI₂, THF/MeOH (20:1), rt, 83%; (g) ethylene glycol, TMSCl, CH₂Cl₂, rt, 91%; (h) EtSH, AlMe₃, CH₂Cl₂, 0 °C to rt; (i) DMP, CH₂Cl₂, rt, 65% over two steps (72% brsm); (j) 1,3-cyclohexanedione (15), Hantzsch ester, L-proline, CH₂Cl₂; then TBDPSCl, Et₃N, CH₂Cl₂, rt, 82%; (k) Pd/C, Et₃SiH, CH₂Cl₂, rt, 88%; (l) TBAF, THF, rt, 91% (>20:1 dr); (m) TBSOTf, 2,6-lutidine, CH₂Cl₂, –40 °C, 90%; (n) SmI₂, HMPA, THF/t-BuOH (20:1), rt, 95%. (b) Comparison of the conformational preferences of intermediates 25 and 26. BHT, 2,6-bis(1,1-dimethylethyl)-4-methylphenol; brsm, based on recovered starting material; HMPA, hexamethylphosphoramide; PIDA, iodobenzene diacetate; TBAF, tetra-n-butylammonium fluoride; TBDPSCl, tert-butyl(chloro)diphenylsilane; TBS, tert-butyldimethylsilyl; TBSOTf, tert-butyldimethylsilyl trifluoromethanesulfonate; THF, tetrahydrofuran; TMSCl, chlorotrimethylsilane.