Chizuko Kabuto

Synthesis of p-tert-Butylthiacalix[4]arene and its Inclusion Property

Abstract A practical method for the synthesis of p-tert-butylthiacalix[4]arene (TC4A), in which the methylene bridges of p-tert-butylcalix[4]arene (C4A) are replaced by epithio groups, is presented by heating a mixture of p-tert-butylphenol, elemental sulfur S8, and NaOH as a base catalyst in tetraethylene glycol dimethyl ether. The inclusion behavior of TC4A for a wide range of solvent molecules is examined by recrystallization, showing preference for the guests depending upon the size and/or the substituent of the guests. The X-ray structure of a 1:2 host–guest complex of TC4A with 1,2-dichloroethane reveals that one guest molecule is included in the cavity of TC4A, while the other is included in the crystal lattice to form a clathrate-type complex. It is shown that the inclusion in the cavity is attained by a cooperative deformation of both the host and the guest.

A stable silicon-based allene analogue with a formally sp -hybridized silicon atom

Carbon chemistry exhibits a rich variety in bonding patterns, with homo- or heteronuclear multiple bonds involving sp-hybridized carbon atoms as found in molecules such as acetylenes, nitriles, allenes and carbon dioxide. Carbons heavier homologues in group 14 of the periodic table—including silicon, germanium and tin—were long thought incapable of forming multiple bonds because of the less effective pπ–pπ orbital overlap involved in the multiple bonds. However, bulky substituents can protect unsaturated bonds and stabilize compounds with formally sp-hybridized heavy group-14 atoms: stable germanium, tin and lead analogues of acetylene derivatives and a marginally stable tristannaallene have now been reported. However, no stable silicon compounds with formal sp-silicon atoms have been isolated. Evidence for the existence of a persistent disilaacetylene and trapping of transient 2-silaallenes and other X = Si = X′ type compounds (X, X′ = O, CR2, NR, and so on) are also known, but stable silicon compounds with formally sp-hybridized silicon atoms have not yet been isolated. Here we report the synthesis of a thermally stable, crystalline trisilaallene derivative containing a formally sp-hybridized silicon atom. We find that, in contrast to linear carbon allenes, the trisilaallene is significantly bent. The central silicon in the molecule is dynamically disordered, which we ascribe to ready rotation of the central silicon atom around the molecular axis.

First direct synthesis of 4,8-dialkylbenzo[1,2-d;4,5-d′]bis[1,2,3]trithioles and 6,10-dialkyl[1,2,3]trithiolo[5,4-h]benzopentathiepins from 1,4-dialkyl-2,3,5,6-tetrabromobenzenes

Abstract New cyclic polysulfides, 4,8-dialkylbenzo[1,2-d;4,5-d′]bis[1,2,3]-trithioles ( 2 ) and 6,10-dialkyl[1,2,3]trithiolo[5,4-h]benzopentathiepins ( 3 ), were directly synthesized by nucleophilic substitution of 1,4-dialkyl-2,3,5,6-tetrahalobenzenes ( 1 ) with elemental sulfur in liquid ammonia.

ENANTIOSELECTIVE ADDITION OF DIETHYLZINC TO ALDEHYDES USING 2-AZANORBORNYLMETHANOLS AND 2-AZANORBORNYLMETHANETHIOL AS A CATALYST

Abstract Optically active 2-azanorbornylmethanols and 2-azanorbornylmethanethiol were prepared from ethyl (1 S ,3 S ,4 R )-2-[( R )-1-phenylethyl]-2-azabicyclo[2.2.1]hept-5-ene-3-carboxylate and catalyzed the enantioselective addition of diethylzinc to aldehydes to give optically active secondary alcohols.

Introduction of Clutch Function into a Molecular Gear System by Silane−Silicate Interconversion

Introduction of the clutch-declutch mechanism into a new gear system, bis(4-methyl-9-triptycyl)difluorosilane 1, is achieved by the reversible attachment of fluoride ion giving the corresponding fluorosilicate 2. Although the phase isomers of 1 (1(dl) and 1(meso)) cannot be separated because of the equilibrium via a slow gear slippage process (DeltaH(double dagger) = 17.2 +/- 0.2 kcal x mol(-1) and DeltaS(double dagger) = 0.9 +/- 0.9 cal x mol(-1) x K(-1)), 1 works as meshed molecular gears in solution at room temperature. On the other hand, silicate 2 in the solid state has quite an unusual TBP structure having two organic triptycyl groups at the apical positions and three electronegative fluorine atoms at the equatorial positions against the Muetterties rule. Rotation of the two triptycyl groups around Si-C bonds in 2 is facile and independent to each other in solution. Silicate 2 is reverted to the corresponding silane mixture by treating with excess water.

Macrocyclic Amides Consisting of Helical Chiral 1,12-Dimethylbenzo[c]phenanthrene-5,8-dicarboxylate.

Helical chiral 1,12-dimethylbenzo[c]phenanthrene-5,8-dicarboxylic acid was synthesized and resolved in multigram quantities. The absolute configuration was determined by X-ray analysis of the bis(camphorsultamamide) derivative. A series of optically active macrocyclic amides consisting of the chiral unit and a dianiline spacer were synthesized by one-pot procedures, and their structures were compared by spectroscopy and X-ray crystallography. One of the cycloamides exhibited catalytic activity in the asymmetric addition of diethylzinc to aromatic aldehydes. N-Alkylated derivatives were also synthesized, which possessed folded structures distinct from those of the parent cyclic amides.

Structure of ephedradine A, a hypotensive principle of Ephedra roots

Abstract A novel flavano-flavonol ephedramin A showing the hypotensive activity has been isolated from the crude drug “ma o -kon”, the roots of Ephedra plants. The stereostructure of ephedrannin A has been elucidated as that represented by formula I on the basis of chemical and physical evidence.

Fourteen‐Electron Bis(dialkylsilylene)palladium and Twelve‐Electron Bis(dialkylsilyl)palladium Complexes

Stable transition-metal complexes with divalent silicon ligands (silylene complexes) have been extensively studied because of their important role in many catalytic processes. Since the pioneering works by Zybill et al. and Tilley et al. , various base-stabilized and base-free silylene complexes have been synthesized and their versatile reactivity has been well explored. Although complexes with two or more silylene ligands are expected to show interesting bonding properties and reactivities that are not observed in monosilylene complexes, such complexes are still limited to donorbridged bis(silylene) complexes and complexes having cyclic diaminosilylenes as ligands. During the course of our study on the application of dialkylsilylene 1, which is the

Crystal structure and inclusion property of p-tert-butylthiacalix[6]arene

Abstract Although the reaction of p-tert-butylphenol with elemental sulfur in the presence of CsOH as a base catalyst yielded a complex mixture comprised of sulfur-bridged phenol oligomers, p-tert-butylthiacalix[6]arene (TC6A) could be isolated in an appreciable yield (0.8%). The X-ray analysis revealed that TC6A adopted a distorted cone conformation stabilized by two sets of hydrogen bondings comprising three phenolic OH groups. The recrystallization from various solvents showed that TC6A had higher inclusion ability toward more guests than TC4A did, suggesting that the expanded central cavity and/or the crystal lattice of the former allowed a more comfortable accommodation of the guest molecules.

Dinuclear titanium(IV) complex of p-tert-butylthiacalix[4]arene as a novel bidentate Lewis acid catalyst

Abstract Treatment of p - tert -butylthiacalix[4]arene (H 4 L, 2 ) with TiCl 4 in dichloromethane gave two novel dinuclear titanium(IV) complexes formulated as [Ti 2 LCl 4 ]. One of the complexes was subjected to X-ray crystallographic analysis to show that the calixarene ligand (L 4− ) adopted a cone conformation, forcing the two metal centers to reside in close vicinity with syn arrangement with respect to the mean plane defined by the macrocycle ( 3 ). The other one was assigned to be an anti titanium(IV) complex ( 4 ) based on 1 H NMR spectroscopy. The syn complex showed high catalytic activity in the Mukaiyama–aldol reaction of aromatic aldehydes with silyl enol ethers, indicating the double-activation ability of the bidentate Lewis acid toward the aldehydes.