Reagents and conditions: (a) tetramethylethylenediamine
(TMEDA), n-BuLi, THF, −75 °C, 2 h; (b)
Me3SiCl, THF, −75 °C, overnight; (c) AlCl3, CH2Cl2, 0 °C; (d) 4-chlorobutanoyl
chloride, −80 to −10 °C, 4 h; (e) NaN3, DMF, 50 °C, 16 h; (f) hydrazine monohydrate, dimethoxyethane
(DME), reflux, 17 h; (g) NaH, DMF, 0 °C, 30 min to 1 h; (h) cyclopentylmethyl
bromide, DMF, 0 °C to rt, 1 to 2 h; (i) SnCl2, CH3OH, 2.5 h; (j) ethyl-2-chloroacetamidate·HCl, Et3N, CH3OH, rt, 1 to 2 h.