A process for the preparation of a compound of formula IA wherein A 1, A 2, A 3 and A 4 are independently of one another C-H, C-R 3, or nitrogen; B is O or CH 2; R 1 is C 1 -C 8 haloalkyl; R 2 is aryl or aryl substituted by one to five R 4, or heteroaryl or heteroaryl substituted by one to five R 4; each R 3 is independently halogen, cyano, nitro, C 1 -C 8 alkyl, C 3 -C 8 cycloalkyl, C 1 -C 8 haloalkyl, C 2 -Csalkenyl, C 2 -C 8 haloalkenyl, C 2 -C 8 alkynyl, C 2 -C 8 haloalkynyl, C 1 -C 8 alkoxy, C 1 -C 8 haloalkoxy, C 1 -Csalkoxycarbonyl-, amino, hydroxy, mercapto, C 1 -C 8 alkylthio, C 1 -C 8 haloalkylthio, C 1 -Csalkylsulfinyl, C 1 -C 8 haloalkylsulfinyl, C 1 -C 8 alkylsulfonyl, C 1 -C 8 haloalkylsulfonyl, C 1 -Csalkylcarbonyl, or two R 3 on adjacent carbon atoms together form a -CH=CH-CH=CH- bridge or a-N=CH-CH=CH- bridge; each R 4 is independently halogen, cyano, nitro, C 1 -C 8 alkyl, C 1 -C 8 haloalkyl, C 2 -C 8 alkenyl, C 2 -C 8 haloalkenyl, C 2 -C 8 alkynyl, C 2 -C 8 haloalkynyl, hydroxy, C 1 -C 8 alkoxy, C 1 -C 8 haloalkoxy, mercapto, C 1 -C 8 alkylthio, C 1 -C 8 haloalkylthio, C 1 -C 8 alkylsulfinyl, C 1 -C 8 haloalkylsulfinyl, C 1 -C 8 alkylsulfonyl, C 1 -C 8 haloalkylsulfonyl, C 1 -C 8 alkylcarbonyl, C 1 -C 8 alkoxycarbonyl, aryl or aryl substituted by one to five R 5, or heterocyclyl or heterocyclyl substituted by one to five R 5; each R 5 is independently halogen, cyano, nitro, C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, C 1 -C 4 alkoxy-, or C 1 -C 4 haloalkoxy-; n is 0, 1 or 2; comprising preparing a compound of formula IV by either a. reacting a compound of formula II with a source of cyanide in the presence of water to give a compound of formula III b. reducing the compound of formula III with a suitable reducing agent to give a compound of formula IV c-i. reacting the compound of formula IV with a compound of formula V wherein R is OH, C 1 -C 6 alkoxy or Cl, F or Br, and R 1, R 2, B, A 1, A 2, A 3 and A 4 are as defined for compounds of formula IA to give a compound of formula I; or or c-ii reacting the compound of formula IV with a compound of formula VI wherein X B is a leaving group for example a halogen, such as bromo, and R 1, R 2, B, A 1, A 2, A 3 and A 4 are as defined for compounds of formula IA with carbon monoxide in the presence of a suitable catalyst to give a compound of formula IA; and wherein the method optionally comprises oxidizing the sulfur atom of the thietane moiety. A 1, A 2, A 3 and A 4 are independently of one another C-H, C-R 3, or nitrogen; B is O or CH 2; R 1 is C 1 -C 8 haloalkyl; R 2 is aryl or aryl substituted by one to five R 4, or heteroaryl or heteroaryl substituted by one to five R 4; each R 3 is independently halogen, cyano, nitro, C 1 -C 8 alkyl, C 3 -C 8 cycloalkyl, C 1 -C 8 haloalkyl, C 2 -Csalkenyl, C 2 -C 8 haloalkenyl, C 2 -C 8 alkynyl, C 2 -C 8 haloalkynyl, C 1 -C 8 alkoxy, C 1 -C 8 haloalkoxy, C 1 -Csalkoxycarbonyl-, amino, hydroxy, mercapto, C 1 -C 8 alkylthio, C 1 -C 8 haloalkylthio, C 1 -Csalkylsulfinyl, C 1 -C 8 haloalkylsulfinyl, C 1 -C 8 alkylsulfonyl, C 1 -C 8 haloalkylsulfonyl, C 1 -Csalkylcarbonyl, or two R 3 on adjacent carbon atoms together form a -CH=CH-CH=CH- bridge or a-N=CH-CH=CH- bridge; each R 4 is independently halogen, cyano, nitro, C 1 -C 8 alkyl, C 1 -C 8 haloalkyl, C 2 -C 8 alkenyl, C 2 -C 8 haloalkenyl, C 2 -C 8 alkynyl, C 2 -C 8 haloalkynyl, hydroxy, C 1 -C 8 alkoxy, C 1 -C 8 haloalkoxy, mercapto, C 1 -C 8 alkylthio, C 1 -C 8 haloalkylthio, C 1 -C 8 alkylsulfinyl, C 1 -C 8 haloalkylsulfinyl, C 1 -C 8 alkylsulfonyl, C 1 -C 8 haloalkylsulfonyl, C 1 -C 8 alkylcarbonyl, C 1 -C 8 alkoxycarbonyl, aryl or aryl substituted by one to five R 5, or heterocyclyl or heterocyclyl substituted by one to five R 5; each R 5 is independently halogen, cyano, nitro, C 1 -C 4 alkyl, C 1 -C 4 haloalkyl, C 1 -C 4 alkoxy-, or C 1 -C 4 haloalkoxy-; n is 0, 1 or 2; a. reacting a compound of formula II with a source of cyanide in the presence of water to give a compound of formula III b. reducing the compound of formula III with a suitable reducing agent to give a compound of formula IV c-i. reacting the compound of formula IV with a compound of formula V wherein R is OH, C 1 -C 6 alkoxy or Cl, F or Br, and R 1, R 2, B, A 1, A 2, A 3 and A 4 are as defined for compounds of formula IA to give a compound of formula I; or or c-ii reacting the compound of formula IV with a compound of formula VI wherein X B is a leaving group for example a halogen, such as bromo, and R 1, R 2, B, A 1, A 2, A 3 and A 4 are as defined for compounds of formula IA with carbon monoxide in the presence of a suitable catalyst to give a compound of formula IA; and wherein the method optionally comprises oxidizing the sulfur atom of the thietane moiety.