Process for the preparation of 1-aryl-3-cyclopropyl-1,3-propanediones

A process for the preparation of a compound of formula (I):

• wherein:
• R2 is C1-6 straight- or branched- chain alkylthio, C1-6 alkyl, C1-6 haloalkyl, CH2SR5, C1-6 alkoxy, C1-6 haloalkoxy, or halogen;
• or an imidazole, pyrazole, 1,2,3,4-tetrazole, 1,2,3-triazole or 1,2,4-triazole ring wherein a ring nitrogen is directly bonded to the benzene nucleus, which ring systems are optionally substituted by one or more groups selected from halogen, C1-6 alkyl, C1-6 haloalkyl or C1-6 straight- or branched- chain alkylthio;
• R3 is C1-6 straight- or branched- chain haloalkyl, C1-6 straight- or branched- chain alkyl, C1-6 alkoxy, C1-6 haloalkoxy, halogen, C1-6 straight- or branched- chain alkylthio or nitro;
• or an imidazole, pyrazole, 1,2,3,4-tetrazole, 1,2,3-triazole or 1,2,4-triazole ring wherein a ring nitrogen is directly bonded to the benzene nucleus, which ring systems are optionally substituted by one or more groups selected from halogen, C1-6 alkyl, C1-6 haloalkyl and C1-6 straight- or branched- chain alkylthio;
• R4 is hydrogen, C1-6 straight- or branched- chain haloalkyl, C1-6 straight- or branched- chain alkyl, C1-6 alkoxy, C1-6 haloalkoxy, halogen, C1-6 straight- or branched- chain alkylthio;
• or a 5 or 6-membered heterocyclic ring which may be unsaturated or partially saturated having 1 to 3 hetero atoms selected from oxygen, nitrogen and sulphur, optionally substituted by halogen, C1-6 haloalkyl, C1-6 alkyl, C1-6 haloalkoxy, C1-6 alkoxy, SOnR5, nitro or cyano;
• or
• R3 and R4 together with the carbon atoms to which they are attached, form a 5 to 7 membered saturated or unsaturated heterocyclic ring having up to three ring heteroatoms selected from nitrogen, oxygen and sulfur, which ring is optionally substituted by one or more groups selected from halogen, nitro, C1-6 straight- or branched- chain alkylthio, C1-4 alkyl, C1-4 alkoxy, C1-4 haloalkyl, C1-4 haloalkoxy, ═O and ═NO—R5;
• and
• R5 represents C1-6 straight- or branched- chain alkyl;
• and
• n represents zero, one or two;
• which process comprises reaction a compound of formula (II):
• wherein R1 is C1-6 straight- or branched- chain alkyl, and R2, R3 and R4 are as hereinbefore defined, with a compound of formula (III):
• in an aprotic solvent in the presence of a base, wherein an alcohol R1OH formed during the reaction is removed by distillation or by a molecular sieve.