A tandem reaction of <i>in situ</i> generated α-amino aldehydes with dimethyloxosulfonium methylide under Corey–Chaykovsky reaction conditions proceeds efficiently to give 4-hydroxypyrazolidine derivatives in high yields with excellent enantio- and diastereoselectivities. This organocatalytic sequential method provides for the efficient synthesis of <i>anti-</i>1,2-aminoalcohols, structural subunits present in several bioactive molecules as well
