Chiral recognition by configurationally chiral cryptands

Abstract

enedi-D-mannitol [ D D -( ~) ] exhibit enantiomeric diff erentiation in complexation equilibria towards ( &) -(BS)-aphenylethylammonium hexafluorophosphate.RECENTLY the first steps have been taken by chemistslJ towards synthesizing organic catalysts which will exhibit the characteristics of regioselectivity and stereoselectivity in catalysing chemical reactions that are normally associated with enzyme-catalysed transformations found in Nature. The availability3 of optically pure configurationally chiral cryptands ~~-( 1 ) -( 3 )and 0~-( 4)-( 6) which are derived from relatively inexpensive sources of chirality and which complex primary alkylammonium cations has prompted us to examine their chiral recognition properties towards (+)-(I?)-, (-)-(S)-, and ( f )-(RS)-a-phenylethylamine Cryptands (1)-(6) all have D, symmetry and conse-

Chiral recognition in NMR spectroscopy using crown ethers and their ytterbium(III) complexes

“…The ester and acid forms of 1a [29] and 1e [30] were prepared according to literature procedures. The nitrate salt of ytterbium(III) [31], tris (6,6,7,7,8,8,8- 1,4,7,10,13,3,11, Compound 1b was prepared by a modification of a literature procedure [30]. (S)-(-)-1-phenylethylamine (0.460 g, 3.8 mmol) and triethylamine (0.380 g, 3.8 mmol) were dissolved in dry methylene chloride (15 ml) and maintained at 0°C under a nitrogen atmosphere.…”

“…This will cause different time-averaged solvation environments that may contribute to chiral recognition in the NMR spectrum. Chiral crown ethers have been an important group of host compounds for the enantiodiscrimination of protonated primary amines [6,7,8,9,10,11]. More recently, a chiral crown ether with a larger cavity was used for the chiral discrimination of secondary amines [12].…”

Sugar Derived Crown Ethers and Their Analogs: Synthesis and Properties

“…Stoddart reported on the synthesis of chiral crowns from the readily available derivatives of 4,6-O-benzylidene-D-pyranoside [6,[8][9][10]. An example of conversion of such diols into the crown ethers is shown in Scheme 1.…”

“…No wonder, that such chirons were used for the preparation of enantiomerically pure macrocyclic receptors. In 1975 a paper by Stoddart, describing synthesis of chiral crown ethers with incorporated sugar unit appeared in the literature [5], and was quickly followed by further papers from this group [6][7][8][9][10]. Variety of oxymethylene units present in each molecule of simple sugars (or their derivatives), allows to incorporate monosaccharides into the structure of crown ethers, which differ in size and flexibility of the macrocyclic ring.…”

Macrocyclic Ligands on Polymers

“…Moreover many of the macrocyclic ligands interact with organic cations such as primary ammonium and diazonium ions, and even with neutral molecules such as urea and acetonitrile. The synthesis of macrocycles with chiral recognition properties (4)(5)(6)(7) has extended their use to the resolution of racemic mixtures and to the mimicry of enzyme systems (8,9). Further developments in macrobicyclic and tricyclic cryptands (2) led to anion Inclusion complexes (10) as well as binuclear complexes where small molecules can be inserted between two bound catlons fixed at a specific distance in the cryptate complex (11).…”