Abstract
1,3‐Dipolar cycloaddition (1,3‐DC) between acryloyloxazolidone 1 and diphenylnitrone 2 was catalysed by complexes of three (4__R__)‐phenylbis(oxazolines) [box = bis(oxazolines)] − either 5‐unsubstituted (8a), or 4,5‐cis‐ and ‐trans‐diphenyl‐substituted (8b, 8c) − with several perchlorates of divalent cations. Normal endo selectivity was obtained with Mg^II^‐ and Ni^II^‐8a catalysts, and the formation of the endo enantiomers (3′R,4′S)‐ or (3′S,4′R)‐3 depended upon the presence of 4‐Å molecular sieves (MS). Different results were observed with the catalysts derived from this ligand and Co^II^ or Zn^II^, which gave good levels of exo enantioselectivity, with 84% ee of (3′S,4′S)‐4. When 8c was used as ligand, Mg^II^, Co^II^ and Ni^II^ give exo‐selective catalysts, and the enantiomer (3′R,4′R)‐4 was obtained with good dr and excellent ee. The unknown absolute configuration of the exo enantiomers 4 was established by structure correlation with one exo diastereoisomer obtained from the 1,3‐DC between 2 and (S)‐3‐acryloyl‐4‐benzyl‐2‐oxazolidinone (10). The flexibility of the catalysts derived from box 8a and 8c, all with 4__R__ configuration, is remarkable since a change in the cation allows the endo‐3 or the exo‐4 enantiomers to be obtained enantioselectively with __ee__s in the 84−99% range. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)