To a solution of 1-{7-[(tert-butoxycarbonyl)amino]-2-methyl-1-oxo-2,3-dihydro-1H-isoindol-4-yl}but-3-en-1-yl acetate (Compound 243E, 895 mg, 2.39 mmol) in DCM (30 mL) were added indium tribromide (85 mg, 0.24 mmol), followed by the addition of allyltrimethylsilane (550 mg, 4.8 mmol) in DCM (0.5 mL). The resulting mixture was refluxed under nitrogen overnight. The solvent was evaporated and the residue was purified by silica gel chromatography (ISCO Combi-flash system, eluting with 10-50% EtOAc/Heptane) to give the desired product as a white solid, 180 mg. The unreacted starting material was recovered and resubjected to the reaction using 2.0 eq. allyltrimethylsilane and 0.2 eq. InBr3. The mixture was refluxed overnight. The solvent was evaporated and the residue was purified by silica gel chromatography (ISCO Combi-flash system, eluting with 10-50% EtOAc/Heptane) to give the desired product as a white solid, 125 mg. Totally 305 mg, 36% yield. 1H NMR (CDCl3): 1.53 (s, 9H), 2.34-2.47 (m, 4H), 2.67 (m, 1H), 3.16 (s, 3H), 4.27 (s, 2H), 4.92-4.99 (m, 4H), 5.55-5.64 (m, 2H), 7.29 (d, J=8.6 Hz, 1H), 8.16 (d, J=8.6 Hz, 1H), 9.52 (br s, 1H). MS (ES+): m/z=379.13 [MNa+]. HPLC: tR=4.83 min (ZQ3, polar—5 min).
