Scheme 1. Preparation of the quaternary ammonium compound 8a. Reagents and conditions: (a) Boc₂O (3.0 equiv.), TEA (1.1 equiv.), DMAP (0.2 equiv.), DCM, RT, 14 h, 89%; (b) LDA (1.2 equiv.), propargyl bromide 12 (2.5 equiv.), –78 °C to RT, 2 h, THF; (c) TFA (5.0 equiv.), DCM, RT, 16 h; 58% over two steps; (d) LiAlH₄ (3.0 equiv.), THF, 80 °C, 1 h, 85%; (e) PPh₃AuNTf₂ (5 mol%), 14 (2.0 equiv.), MsOH (1.3 equiv.), TFA (1.1 equiv.), AgOTf (2 mol%), DCE, RT, 6 h; then NaHCO₃ (sat.), AgOTf (1.0 equiv.), RT, 73%.