Total spontaneous resolution of a cyanoguanidine showing only conformational chirality

Abstract

The total spontaneous resolution of N-(4-chlorophenyl)-NAcyano-N,NB,NB-trimethylguanidine, a compound which shows only conformational chirality, is described; variable temperature NMR experiments show that rotation of the dimethylamino group is rapid in solution at room temperature as is conformer interconversion by rotation of the arylmethylamino group.

From Molecules to Crystal Engineering: Supramolecular Isomerism and Polymorphism in Network Solids

“…Therefore, an analogy can be drawn with homochiral compounds. This type of supramolecular isomerism lies at the heart of an important issue: spontaneous resolution of chiral solids. − …”

“…This type of supramolecular isomerism lies at the heart of an important issue: spontaneous resolution of chiral solids. [59][60][61][62][63][64][65] The remainder of this contribution reviews the subject of supramolecular isomerism and how it leads to superstructural diversity in network solids. Emphasis is placed upon metal-organic or coordination polymers and organic solids, respectively.…”

Dynamic Helical Chirality of an Intramolecularly Hydrogen-Bonded Bisoxazoline

“…Conformational chirality has been observed primarily in compounds displaying atropisomerism such as helicenes, substituted biphenyls, 1,1‘-bi-2-binaphyls, molecular propellers, “geländer” molecules, transition-metal complexes, and cyclophanes . Occasionally, compounds having chiral conformations with low barriers to racemization spontaneously resolve during crystallization into a single conformational enantiomer but racemize in solution . Although the use of highly rigid, preorganized structures in functional materials and supramolecular chemistry has been a successful design strategy, it has recently been suggested that overly constrained synthetic catalysts and receptors are less effective, because in these rigid systems binding affinity and specificity are interdependent .…”

Crystallization Behavior of Heterotrinuclear ZnII–LnIII–ZnII Complexes Bearing Two Tripodal Nonadentate Ligands: Possibility for Absolute Spontaneous Resolution

“…By contrast, it is well known that ca. 5% of chiral compounds exhibit spontaneous resolution, where it is believed that equal amounts of both enantiomorphic crystals (conglomerates) are deposited. − Recently, an interesting crystallization phenomenon named total spontaneous resolution has been recognized, − in which pure (100% enantiomeric excess) one-handed enantiomorphic crystals were deposited in a crystallization experiment (Figure ) under the conditions of an attrition-enhanced resolution or rapid catalytic racemization taking place in solution. In the cases of some transition-metal or lanthanoid complexes, − no catalyst was required for this phenomenon owing to a rapid ligand-exchange process leading to racemization.…”