Process for the production of cyclic diketones

A process for the preparation of a compound of formula I

• wherein Y is an organic substituent which is so selected that the compound of formula I has a pK value of from 1 to 5;
• A1 is CR1R2;
• A2 is oxygen, C(O), SO2 or (CR3R4)n;
• n is 1 or 2;
• A3 is CR5R6;
• R1, R2, R3, R4, R5 and R6 are each independently of the others C1-C4alkyl which may be mono-, di- or tri-substituted by C1-C4alkoxy, halogen, hydroxy, cyano, hydroxycarbonyl, C1-C4alkoxycarbonyl, C1-C4alkylthio, C1-C4alkylsulfinyl, C1-C4alkylsulfonyl, C1-C4alkylcarbonyl, phenyl or by heteroaryl, it being possible for the phenyl and heteroaryl groups in turn to be mono-, di- or tri-substituted by C1-C4alkoxy, halogen, hydroxy, cyano, hydroxycarbonyl, C1-C4alkoxycarbonyl, C1-C4alkylsulfonyl or by C1-C4haloalkyl, the substituents on the nitrogen in the heterocyclic ring being other than halogen;
• and/or R1, R2, R3, R4, R5 and R6 are each independently of the others hydrogen, C1-C4alkoxy, halogen, hydroxy, cyano, hydroxycarbonyl, C1-C4alkoxycarbonyl, C1-C4alkylthio, C1-C4alkylsulfinyl, C1-C4alkylsulfonyl, C1-C4alkylcarbonyl, phenyl or heteroaryl, it being possible for the phenyl and heteroaryl groups in turn to be mono-, di- or tri-substituted by C1-C4alkoxy, halogen, hydroxy, cyano, hydroxycarbonyl, C1-C4alkoxycarbonyl, C1-C4alkylsulfonyl or by C1-C4haloalkyl, the substituents on the nitrogen in the heterocyclic ring being other than halogen;
• and/or
• R1 and R2 together form a 3- to 5-membered carbocyclic ring which may be substituted by C1-C4alkyl and/or interrupted by oxygen, sulfur, S(O), SO2, OC(O), NR7 or by C(O);
• and/or
• R2 and R4 together or R2 and R5 together form a C1-C3alkylene chain which may be interrupted by oxygen, sulfur, SO, SO2, OC(O), NR8 or by C(O);
• it being possible for that C1-C3alkylene chain in turn to be substituted by C1-C4alkyl;
• and
• R7 and R8 are each independently of the other C1-C4alkyl, C1-C4haloalkyl, C1-C4alkylsulfonyl, C1-C4alkylcarbonyl or C1-C4alkoxycarbonyl;
• in which process
• a) a compound of formula II
• wherein A1, A2 and A3 are as defined for formula I, is reacted with a bromine or chlorine source to form a compound of formula III
• wherein A1, A2 and A3 are as defined for formula I and X is chlorine or bromine;
• b) that compound is reacted with water to form the compound of formula IV
• wherein A1, A2 and A3 are as defined for formula I and X is chlorine or bromine;
• c) that compound is converted, using a compound of formula V
• M+-O−—C(O)—Y, (V)
• wherein Y is as defined hereinbefore and M+ is the hydrogen cation or an alkali metal ion, alkaline earth metal ion or ammonium ion, into the compound of formula VI
• wherein A1, A2, A3 and Y are as defined for formula I, and
• d) then that compound is treated with a cyanide source in the presence of a base.