Synthesis and biological activity of diastereomeric racemates of asymmetric 1,3,2-benzodioxaphosphorin derivatives

New 6-substituted-2-alkoxy (aryloxy)-4-(2, 4-dichlorophenyl) -4H-1,3,2-benz odioxaphosphorin 2-sulfides 3a-3g were synthesized utilizing PTC cyclizatio n reaction. Seven couples of compounds 3a-3g diastereomeric racemates (A an d B) were separated by crystallization. Their structures were confirmed by H-1 NMR, P-31 NMR and elementary analysis, The single-crystal X-ray analysi s of 3a-A indicated that its relative configuration is (2R, 4S; 2S,4R). The preliminary bioassays indicate that compound 3c has a good insecticide act ivity. The diastereomeric racemates A and B show a synergistic insecticide activity.