Process for the preparation of optically active isoxazoline compounds

The present invention relates to a process for the preparation of a compound of formula (I) wherein A1 and A2 are C-H, or one of A1 and A2 is C-H and the other is N; R1 is C1-C4alkyl, C1-C4haloalkyl or C3-C6cycloalkyl; each R2 is independently bromo, chloro, fluoro or trifluoromethyl; R3 is hydrogen; R4 is hydrogen, halogen, methyl, halomethyl or cyano; or R3 and R4 together form a bridging 1,3-butadiene group; R5 is chlorodifluoromethyl or trifluoromethyl; n is 2 or 3; by reacting a compound of formula (II) wherein A1, A2, R1, R2, R3, R4, R5 and n is as defined under formula (I) above, with hydroxylamine, a base and a chiral catalyst, characterized in that the chiral catalyst is a dimeric chiral catalyst of formula (III) wherein R6, R7, R8, R9, R10 and X are as defined in claim 1.