aReagents and conditions: a) CDI, CH3CN, rt, 30 min, R1CH(CO2Et)(CO2K), Et3N–MgCl2, rt, overnight; b) Zn, THF; c) thiourea, EtONa, EtOH, refluxing for 8h; d) ClCH2COOH, AcOH, H2O, refluxing, overnight; e) CH3C(OTMS)=NTMS (BSA), substituted benzyl alcohol, (HCHO)n, TMSCl, TBAI ( cat.), CH2Cl2, rt, 70–90%; f) NaH, mCPBA, THF, rt.