To a solution of 3-t-butyldiphenylsilyloxy-1-(4-ethoxycarbonyl-1,3-thiazol-2-yl)azetidine (5.85 g, 12.5 mmol) (obtained as described in Reference Example 2(1)) in benzene (290 ml) was added a solution of 0.67M ammonium chloride-trimethylaluminium in benzene (56.4 ml) at room temperature under an atmosphere of nitrogen. The mixture was stirred in a water bath (40° C.) for 17 hours. After checking the completion of the reaction, 10% aqueous acetic acid solution (100 ml) and ethyl acetate (50 ml) were added to the reaction mixture in an ice bath and the resulting mixture was stirred at room temperature for 2 hours. After adding ethyl acetate thereto, the reaction mixture was partitioned between ethyl acetate and water. The organic layer was washed successively with saturated aqueous sodium hydrogencarbonate solution and saturated aqueous sodium chloride solution, dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure. The residue was purified by chromatography on a silica gel column using toluene:acetonitrile (3:1→1:2) as the eluant to afford 3-t-butyldiphenylsilyloxy-1-(4-carbamoyl-1,3-thiazol-2-yl)azetidine (4.97 g, yield 91%) as a pale brown solid.
