Enantioselective Aldol Reactions in Water by a Proline-Derived Cryptand and Fixation of CO by Its Exocyclic Co(II) Complex.

The secondary amine donors present in the bridges of a laterally nonsymmetric oxa-aza cryptand have been derivatized with l-proline to obtain the chiral cryptand L. The cryptand L efficiently catalyzed aldol reactions in water with up to 75% ee. On reacting with Co(II) perchlorate in the presence of KSCN, L readily formed the trinuclear complex {[Co(L)(NCS)]·(15CHCN)(5acetone)(6HO)} (1). The complex 1 in combination with the cocatalyst tetrabutylammonium bromide (TBAB) formed an efficient catalytic system in the synthesis of cyclic carbonates from CO and epoxides at room temperature and atmospheric pressure.