Diastereoselective noncovalent synthesis of hydrogen-bonded double-rosette assemblies

Chiral centers present either in the dimelamine components of calix[4]arene I or in the cyanurate components CA quantitatively induce one handedness (P or M) in the corresponding hydrogen-bonded assemblies L. (CA)(6) (de>98%). The high degree of chiral induction results from the presence of six chiral centers in close proximity (C,,) to the core of the assembly. A much lower level of chiral induction is observed for assemblies with chiral centers that are more remote (C,,). All diastereomerically pure assemblies V(CA), exhibit very high CD activities (\Deltaepsilon(max)\similar to100 Lmol(1) cm(-1)). in sharp contrast to the low CD activities (\epsilon(max)\less than or equal to8 Lmol(1) cm(-1)) shown by the free components. The assemblies display spontaneous resolution under thermodynamically controlled conditions (i.e., heteromeric assemblies containing both peripheral R and S centers are not observed. Remarkable assembly behavior is observed if both components I and CA are chiral. In general, formation of well-defined assemblies is only observed when both components contain unidirectional information for the induction of either M or P chirality.