Process for the preparation of n-alkyl-2(hydroxy-4benzoyl)-3 benzofurans and intermediates thereof
Process for the preparation of a 2-(n-alkyl)-3-(4-hydroxybenzoyl)benzofuran of formula (I) in which R represents a linear or branched alkyl radical including from 1 to 5 carbon atoms and R1 represents a linear or branched alkyl radical including from 1 to 3 carbon atoms, a linear or branched alkoxy radical including from 1 to 3 carbon atoms, a halogen atom or a nitro radical, and intermediates.
1. A compound of formula (V)
in which R3 represents a hydroxyl radical or represents a halogen atom, R4 represents a linear or branched alkyl radical including from 2 to 5 carbon atoms and R′ 1 represents a nitro radical.
2. The compound according to claim 1 , characterized in that R′ 1 represents a nitro radical in the 5 position and R4 represents an n-butyl radical.
3. A process for the preparation of a 2-(n-alkyl)-3-carboxybenzofuran of formula (II), characterized in that a 3-(1-hydroxyalkylidene)-3H-benzofuran-2-one of formula (VI):
or its 3-alkanoyl-3H-benzofuran-2-one ketonic tautomeric form of formula (VII):
in which R4 represents a linear or branched alkyl radical including from 2 to 5 carbon atoms and R′ 1 represents a nitro radical, is treated by heating and by an acid catalyst in concentrated aqueous solution of at least 80% by weight and then the expected product of formula (II)
is isolated.
4. Process according to claim 3 , characterized in that the treatment by heating of the compound of formula (VI) or of formula (VII) is carried out in a carboxylic acid.
5. The process of claim 3 , wherein the acid catalyst in concentrated aqueous solution is concentrated sulphuric acid at between 80% and 95% by weight.