Boron tribromide → Apigenin dimethylether

HRID 1976346Notes

Reaction equation

HRID 1976346 reaction equation
[Tl+].[CH3:2][O:3][C:4]1[CH:9]=[CH:8][C:7]([C:10]2[O:20][C:19]3[C:14](=[C:15]([O:23]C)[CH:16]=[C:17]([O:21][CH3:22])[CH:18]=3)[C:12](=[O:13])[CH:11]=2)=[CH:6][CH:5]=1.B(Br)(Br)Br>>[CH3:2][O:3][C:4]1[CH:5]=[CH:6][C:7]([C:10]2[O:20][C:19]3[C:14](=[C:15]([OH:23])[CH:16]=[C:17]([O:21][CH3:22])[CH:18]=3)[C:12](=[O:13])[CH:11]=2)=[CH:8][CH:9]=1

Participants

4

Reactant 3

HCID 25134Boron tribromide2×HCID 797305,7,4'-TrimethylapigeninHCID 105005Thallous cation

Product 1

HCID 5281601Apigenin dimethylether

Procedure

The desired 6-iodinated species was prepared in excellent yield with almost exclusive regioselectivity by exploiting the ortho-directing capabilities of thallium(I) salts in the iodination of phenols14 (Scheme 2). Selective demethylation of apigenin trimethyl ether (5b) in the 5-position may be accomplished with boron tribromide in an amount generally ranging between about 0.9 equiv and about 3.0 equiv, preferably about 1.1 equiv boron tribromide, to afford apigenin 7,4′-dimethyl ether (6). The reaction is generally carried out a temperature ranging between about −40° C. and about 50° C., preferably about 25° C., for a time period ranging between about 0.5 h and about 24 h, preferably about 5 h, in the presence of a suitable solvent such as methylene chloride, chloroform, benzene and toluene, preferably methylene chloride, until a thick precipitate is formed. The precipitate is then collected and recrystallized in a suitable solvent such as ethanol, methanol, ethyl acetate/hexane, preferably ethanol. If desired, other boron compounds such as boron trichloride may be used in place of boron tribromide29.

Workup

  1. customThe desired 6-iodinated species was prepared
  2. customin excellent yield with almost exclusive regioselectivity

Sources & evidence

ORD record
ord-666bbc71f3d747cd9d49353096954c72
Source dataset
uspto-grants-2001_05
Patent number
US06225481B1

Reaction notes

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