The syntheses of simplactones (3R,4S)-1 and (3R,4R)-2 were achieved in 5 steps from N-acyl thiazolidinethione chiral auxiliaries. The syntheses feature a double diastereoselective acetate aldol reaction solely controlled by the chirality of the auxiliary. Highly diastereoselective aldol reactions with s-trioxane were also achieved with N-acyl thiazolidinethione auxiliaries and the stereochemistry of an aldol product confirmed by X-ray analysis.