The invention discloses a preparation method of a key intermediate of baloxavir marboxil. The preparation method comprises the following steps: carrying out a
nucleophilic substitution reaction on polysubstituted 2,3-difluoro-6-halogenated
benzyl alcohol represented by a formula (I) to synthesize 2,3-difluoro-6-halogenated benzyl
halide represented by a formula (II), carrying out a
nucleophilic substitution reaction on the polysubstituted benzyl
halide represented by the formula (II) to synthesize 2,3-difluoro-6-halogenated benzyl phenylsulfide represented by a formula (III), carrying out a
Grignard reaction on the polysubstituted benzyl phenylsulfide represented by the formula (III) to synthesize 3,4-difluoro-2-(phenylthio)methyl)
benzoic acid represented by a formula (IV), and carrying out a Friedel-Crafts
acylation reaction on the polysubstituted
benzoic acid to synthesize 7,8-difluorodibenzo[b,e]
thiophene-11(6H)-one represented by a formula (V). In the formula (I), the formula (II)and the formula (III), X<1> and X<2> are separately and independently selected from
chlorine,
bromine or
iodine. According to the preparation method, the polysubstituted
benzyl alcohol is used as a starting
raw material, and the steps of two-step
nucleophilic substitution, Grignard exchange, Friedel-Crafts
acylation and the like are carried out to prepare the key intermediate of the anti-influenzadrug baloxavir marboxil, so that original innovation is achieved.