Method for producing 4-borono-L-phenylalanine and intermediate thereof

A method for producing a compound of formula (II) from a compound of formula (I):

• wherein, in formulas (I) and (II),
• X is selected from the group consisting of Cl, F, Br and I,
• R1 is NR11R12, R11 is selected from the group consisting of H and a protecting group for an amino group, and R12 is a protecting group for an amino group,
• R2 is COOR21, and R21 is selected from the group consisting of H, a linear or branched C1-C10 alkyl group, and a benzyl group,
• R3 is selected from the group consisting of H and COOR31, and R31 is selected from the group consisting of a linear or branched C1-C10 alkyl group and a benzyl group, and
• R4 is selected from the group consisting of boronic acid (B(OH)2), a boronic acid ester, and a boronic acid amide,
• the method comprising:
• a first step of reacting the compound of formula (I) with a linear or branched C1-C10 alkylmagnesium halide in the presence of a metal halide at a reaction temperature in a range of −50° C. to −20° C.;
• and
• a second step of reacting the compound obtained in the first step and a boric acid ester or a boric acid amide at a reaction temperature in a range of −50° C. to −20° C., thereby producing the compound of formula (II).