Scheme 4. General Preparation of 15a, 15b, 19a, 19b, 20–22, and 25.

Reagents and conditions: (a) MeI, NaHCO₃, DMF, MW 120 °C, 45 min, 93% for 52, 85% for 25; (b) NaH, MeI, DMF, 0 °C, 1 h, 67% for 53; (c) Mg, MeOH, rt., 16 h, 66% for 21, 72% for 22; (d) NaOH, MeOH, 70 °C, 4 h, 91% for 19b, 87% for 20, 77% for 15b; (e) TMDA, (CHO)_n, 1,4-dioxane, MW 140 °C, 40 min and then NaBH₃CN, EtOH, reflux, 14 h, 62% for 19a, 75% for 15a; (f) see Ville et al.;³⁹ (g) NaClO₂, H₂NSO₃H, 2-methyl-2-butene, 1,4-dioxane/H₂O (1:1), 0 °C, 2 h, quant.; (h) see Viault et al.⁴⁷