A solution of 266 mg (0.891 mmol) of 4-(4-amino-3-cyclohex-1-enyl-phenyl)-1-methyl-piperidine-2,6-dione (as prepared in the previous step) in CH2Cl2 (10 mL) was treated with 623 mg (1.34 mmol) of PyBroP, 300 mg (0.981 mmol) of 4-cyano-1-(2-trimethylsilanyl-ethoxymethyl)-1H-imidazole-2-carboxylate potassium salt (as prepared in Example 1, step (d)), and 466 μL (2.67 mmol) of DIEA at RT for 16 h. The mixture was diluted with CH2Cl2 (30 mL) and washed with saturated aqueous NaHCO3 (1×30 mL). The organic layer was dried (MgSO4) and concentrated in vacuo. Silica gel chromagography of the residue on a 50-g Varian MegaBond Elut SPE column with 25% EtOAc-hexane afforded 130 mg (27%) of the title compound as an off-white solid: Mass spectrum (ESI, m/z): Calcd. for C29H37N5O4Si, 548.3 (M+H). found 547.9.
