Synthesis of new enantiomerically pure C-1- and C-2-symmetric N-alkyl-benzimidazolium and thiazolium salts

Starting from the commercially available enantiopure (1S,2S)-2-amino-1- phenyl-1,3-propanediol novel enantiomerically pure benzimidazoles were prepared; N-alkylation gave chiral benzimidazolium salts, which were tested in asymmetric benzoin condensations. The synthesis of conceptually new, enantiomerically pure, C2 symmetric bis-thiazolium and bis-benzimidazolium salts was also developed. These new chiral heterocycles were employed as catalysts in the asymmetric dimerisation of benzaldehyde to give benzoin with moderate enantioselectivity.