As a solvent, ether such as diethyl ether or tetrahydrofuran, alcohol such as methanol or ethanol, or water may be used according to the property of the agent.STEP 15In this step, the hydroxy compound 2a(3R*) [2a(3R*-.beta.) or 2a(3R*-.alpha.)] prepared in Steps 11 or 14 is converted into the azide.