Chiral Synthesis via Organoboranes. 46. An Efficient Preparation of Chiral Pyridino- and Thiopheno-18-crown-6 Ligands from Enantiomerically Pure C(2)-Symmetric Pyridine- and Thiophenediols(1).

Asymmetric reduction of 2,6-diacylpyridines with B-chlorodiisopinocampheylborane provides the corresponding C(2)-symmetric diols in very high de and ee. Asymmetric allylboration of 2,6-pyridinedicarboxaldehyde and 2,5-thiophenedicarboxaldehyde provides the corresponding bis-homoallylic alcohols in very high de and ee. These optically pure diols were converted to the disodium or dipotassium salts and treated with tetra(ethylene glycol) ditosylate to obtain the corresponding chiral pyridino and thiopheno-18-crown-6 ligands. However, the perfluoroalkyl diols failed to provide the macrocycles.