David D. MacNicol

An efficient synthesis of hexa-substituted benzenes and the discovery of a novel host conformation for hexakis (β-naphthylthio) benzene

The title host molecule (III) has been synthesised by reaction of hexachlorobenzene with an excess of the sodium salt of β-mercaptonaphthalene in 1,3-dimethyl-2-imidazolidinone (DMEU) as solvent; other hexakis (arylthio)- benzenes, hexakis(phenoxy) benzene (IV), and hexakis (phenylseleno) benzene (V) were prepared analogously from hexahalobenzenes, HMPA being used as solvent in the last case. An X-ray analysis of the channel-type adduct of (III) with 1,4-dioxan as guest reveals a unique host conformation in which the side-chains are not situated alternately above and below the plane of the central benzene ring.

Vibrational Raman optical activity of cyclodextrins

Vibrational Raman optical activity spectra of aqueous solutions of α−, β− and γ-D-cyclodextrin in the range 700–1500 cm−1 are reported. As well as showing features characteristics of D-glucose, the ROA spectra all show remarkably intense features between 890 and 960 cm−1 originating in coupled C(1)-H deformations and glycosidic C-O stretches delocalized around the cyclodextrin ring and which reflect the stereochemistry of the glycosidic links.

Cyclodextrins as chiral nuclear magnetic resonance shift reagents

Although chemical shift non-equivalence between enantiotopic groups in n.m.r. spectra has often been observed employing optically active solvents or chiral lanthanide shift reagents, or when a substrate is complexed to a chiral crown compound, such methods are normally critically dependent upon suitable substrate functionality. We now report that guest binding within the chiral cavity of β-cyclodextrin in D2O provides a method for inducing 19F n.m.r. chemical shifts between the prochiral CF3 groups of compounds 1 [1,1,1,3,3,3-hexafluoro-2-phenyl-2-propanol] and 2 [1,1,1,3,3,3-hexafluoro-2-(p-tolyl)propane], it being particularly noteworthy that the latter molecule lacks the type of functional group usually required for such chiral effects.

New strategy for the design of inclusion compounds:discovery of the ‘hexa-hosts’

A novel concept for the design of inclusion compounds, which has lead to the discovery of a series of hosts, is described.

Synthesis of hexakis(aryloxy)benzenes: x-ray analysis of hexakis (phenyloxy) benzene and of the acetonitrile clathrate of hexakis (3,5-dimethylphenyloxy) benzene

Abstract Hexakis (aryloxy) benzenes (I)-(IV), representatives of a new class of molecule, have been prepared by reaction of hexafluorobenzene with the sodium salt of the appropriate phenol in 1,3-dimethyl-2-imidazolidinone (DMEU) as solvent. X-ray analyses of parent (I) and of the acetonitrile clathrate of (II) are described, a novel edge-on interaction between host and guest being found in the latter.

Chiral host–guest complexes: interaction of α-cyclodextrin with optically active benzene derivatives

The binding to α-cyclodextrin of a series of small, chiral benzene derivatives has been studied by direct reaction microcalorimetry and by a spectral competitive inhibition technique. A small, but distinct, chiral discrimination is demonstrated in the binding of the optical isomers of phenylalanine and α-methylbenzylamine, whereas mandelic acid, amphetamine, and phenyltrifluoroethanol show no such effect. The enthalpies of complex formation are remarkably similar for all compounds studied, ΔH ca.–3.5 kcal mol–1(25 °C; pH 11.0; 0.1M-phosphate buffer). No obvious correlation of chiral effects with molecular structure has been found. It is concluded that insertion of the aromatic ring in the central cavity of α-cyclodextrin provides the major driving force for complex formation, and that chiral interactions external to the cavity are of minimal importance in this class of compounds.

Design and synthesis of rhombohedral clathrates for containment of small, reactive guest species

Abstract The new hexa-hosts hexakis( p -phenoxyphenoxy)benzene 2 and its p -benzylphenoxy analogue 3, targetted at rhombohedral clathrate packing, have been prepared. X-ray measurements have established that 2 and 3 form very similar rhombohedral closed-cage structures with common trigonal space group R 3 . The cavities of these clathrates are potentially useful for the handling of reactive reagents, examples for 2 being phosgene, thiophosgene, thionyl chloride, and methyl iodide.

Crystal and molecular structure of an OH ⋯π hydrogen-bonded system : 2,2-bis-(2-hydroxy-5-methyl-3-t-butylphenyl)propane

The crystal structure of the title compound (I) has been determined by three-dimensional X-ray analysis. Crystals are orthorhombic, a= 14.089, b= 18.190, c= 8.896 A, Z= 4, space group P212121. The structure was solved by direct methods employing 1 646 significant diffractometer data, and refined by least-squares methods to a final R of 0.038. The structure possesses two independent intramolecular OH ⋯π hydrogen bonds, mean 2.09 A, for the perpendicular distance between the hydroxy-hydrogen atom and its corresponding π-electron-dono rring.

Tellurium extrusion: a novel method for carbon–carbon bond formation

Pyrolysis of 9-tellurabicyclo[3,3,1]nona-2,6-diene (II) in [2H8]toluene at 175° leads to loss of elemental tellurium and quantitative formation of bicyclo-[5,1,0]octa-2,5-diene (III) which was also formed independently by the action of Te2– anion on the dibromide (I) during the preparation of (II).

Discovery and X-ray crystal structure of a new host compound: 1,3,4-tris(phenylthio)[1]benzothieno[3,2-c]pyridine

Abstract In 1,3-dimethyl-2-imidazolidinone (DMEU) as solvent, pentafluoropyridine reacts with PhSNa to give an essentially quantitative yield of pentakis(phenylthio)pyridine (1); however, analogous reaction with pentachloropyridine leads to the unexpected conformation of the title compound (2), a new host whose crystal structure has been elucidated by X-ray methods for both the unsolvated crystal and for the chlorobenzene inclusion compound.