AbstractThe 1,3‐dipolar cycloaddition of allyl halides with chiral nitrile oxides, derived from glyceraldehyde derivatives, affords ca. 1:1‐mixtures of C5‐epimeric isoxazolines. The diastereomers can be separated on a preparative scale by MPLC; the configurations at C5 are established by chemical correlation/X‐ray analysis initially, and then routinely, based on consistent, large differences of respective specific rotations. – An unexpected finding, which turned out to be the key to efficient transformation of 5‐halomethyl‐isoxazolines into hydroxy‐pyrrolidines, is that highly stereoselective catalytic hydrogenations are feasible with proper combination of both 3‐ and 5‐side chain structures and the catalyst system. – This (C3 + Cn)‐approach is extended to include dihydroxy‐pyrrolidines, i. e. 1,4‐iminopolyols, and further 1,5‐iminopolyols and bicyclic 1,5,8‐iminopolyols. The substrates for the latter hydrogenation/cyclization are derived from optically active furoisoxazolines. – Some of the new iminopolyols show strong inhibition of glucosidases.