The invention discloses a method for synthesizing a
doxycycline hydrochloride intermediate alpha-6-
doxycycline through hydrogenation on the basis of a
silica gel rhodium catalyst. The invention adopts the key technical scheme that the method comprises the following steps: (1), a
rhodium complex is loaded on functionalization
silica gel to prepare the
silica gel rhodium catalyst; (2), the prepared silica gel rhodium catalyst is dispersed into an
organic solvent, methacycline or the salt of the methacycline is used as a
raw material,
hydrogen is introduced, and the reaction lasts for 4 to 12 hours under the conditions that the pressure is 0.4 to 2.5 MPa and the
reaction temperature is 40 to 120 DEG C, so that the
doxycycline hydrochloride intermediate alpha-6-doxycycline is prepared. The silica gel rhodium catalyst in the invention has high catalytic activity and
enantio selectivity and can be used for
doxycycline hydrochloride production process, the yield can reach more than 60 percent, the content of beta-isomer is only 0.03 percent to 0.10 percent, the reaction condition is mild, the reaction directionality is excellent, side reactions are less, and the catalyst can be reduced, so that the production cost is lowered and the industrial production is facilitated.