Abstract: Two kinds of compounds were synthesized by the reaction of diethoxyisocyanatophosphine with benzalanilines depending at the different positions of substituents attached to the benzene ring.When there was no substituent or the substituent was at m-, or p-position, the normal 1,3-dipolar cy-cloaddition took place to yield a stable compound 2, 1,3,4-diazaphospholidene, through a rearrangement of ethyl from Oatom to Natom.The effects of the reaction temperature and solvent were investigated and the diastereoisomers of compound 2 were separated by TLC.However, when the substituent was at o-position, compound 5, a-anilino phosphonate was obtained under the same experimental conditions.Aconclusion might be drawn that the steric hindrance effect of the ortho substituent block the cycloaddition and the intermediate was hydrolyzed by the moisture.Elementary analysis, ¹H NMR, IRand MSspectra confirmed the structures of the compounds.

Key words: Cycloaddition reaction,1,3,4-Diazaphospholidene, Diethoxyisocyanatophosphine, Ben-zalaniline