Abstract: The condensation of para-substituted aromatic aldehydes with 1, 2-aminoalcohols such as (L)-prolinol, gives 1, 3- oxazolidines (potential proinsecticides). Starting of (S) amino alcohol, thanks to asymmetric carbone C2, we can obtain (S, S) and (S, R) diastereoisomers. The substituent situated on para position to aldehyde function in aromatic ring, affects the obtained proportion on diastereoisomers. If it is an electro-donor, the (S, S) diastereoisomer is clearly dominent; if it is an electro-attractor, the proportion of (S, S) and (S, R) diastereoisomers is practically the same.