The aza-Michaeladdition of enantiopure 1-aminopyrrolidines to (E)-alkenyl sulfones in the presence of a catalytic amount of ytterbium trifluoromethanesulfonate [Yb(OTf)3] yields β-hydrazino sulfones in moderate to good yields and with diastereoselectivities of up to ≥ 98%. The latter undergo reductive N-N bond cleavage with BH3 · THF and, after N-protection with Boc2O or benzyl bromide, afford N-protected