Method for preparing meta-functionalized pyridine compound

A method for preparing a meta-functionalized pyridine compound, the method comprising the following steps:

• S1, preparation of 1,4-dihydropyridine, involving:
• in a glove box filled with nitrogen, adding a catalyst, a solvent, pinacolborane and pyridine to a reaction flask in order and stirring the mixture for a sufficient reaction to obtain 1,4-dihydropyridine, with the reaction formula as follows:
• wherein:
• the catalyst is triarylborane, the molar ratio of the triarylborane to the pyridine is (10-15):
• 100, and the structural formula of the triarylborane is B(R1)3, wherein R1 is phenyl, pentafluorophenyl, 3,5-bis(trifluoromethyl)-substituted phenyl, or 2,4,6-trifluoro-substituted phenyl;
• the equivalent ratio of the pinacolborane to the pyridine is 1.5:1;
• the solvent is tetrahydrofuran, 1,2-dichloroethane or an aromatic solvent;
• and
• the reaction temperature is 40-110° C., and the reaction time is 5-12 hours;
• and
• S2, catalyzed functionalization of pyridine at the meta-position, involving:
• adding an imine, an aldehyde, a ketone or a halogenation reagent to the above reaction flask, and stirring the mixture in a nitrogen atmosphere until the reaction is completed;
• and performing distillation under reduced pressure to remove the solvent and column chromatography separation to obtain a pyridine compound substituted with aminomethyl, hydroxymethyl, benzyl, chlorine or bromine at the meta-position, with the reaction formula as follows:
• wherein the reaction temperature is 40-110° C., and the reaction time is 5-24 hours;
• and
• in the structural formula of the above pyridine, 1,4-dihydropyridine, and pyridine compound substituted with aminomethyl, hydroxymethyl, benzyl, chlorine or bromine at the meta-position, R2 is an alkenyl, aryl, alkyl, halogen, ester or heteroaryl substituent, R3 is alkyl, R4 is tert-butoxycarbonyl or benzyloxycarbonyl, R5 is an aryl, alkyl or heteroaryl substituent, R6 is aryl, R7 is an ester group, R8 is an ester group or trifluoromethyl, and R9 is chlorine or bromine.