Scheme 1. symmetric Synthesis of Cyclohexene Skeletona.
aReagents and conditions: (a) benzaldehyde dimethyl acetal, CSA•H2O, CH2Cl2, −20 °C, 2 h; (b) m-CPBA, CH2Cl2, 0 °C to rt, overnight; (c) 1.0 M LAH in Et2O, Et2O, rt, 20 min; (d) 4-methoxybenzyl chloride, NaH, TBAI, DMF, 0 °C to rt, overnight; (e) TsOH•H2O, CH2Cl2/EtOH (1:5), rt, 24 h; (f) SOCl2, pyridine, CH2Cl2, 0 °C, 20 min; (g) NaN3, DMF, rt, 24 h; (h) Ph3P, THF/H2O (9:1), rt, 19 h; (i) Boc2O, Et3N, 1,4-dioxane/H2O (10:3), rt, 40 min.