Stereocontrolled oxidation of a thiacalix[4]arene to the sulfinyl counterpart of a defined SO configuration (original) (raw)
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Tetrahedron Letters, 2017
The partial S-oxidation of all four basic conformations of thiacalix[4]arene was carried out using NaBO 3 Á4H 2 O as the oxidizing agent. It was found that despite the possible formation of many regioand stereoisomers, the reactions leading to mono-or disulfoxides were highly regio-and stereoselective depending on the starting conformation. Our results clearly show that the sulfur atoms possessing synorientation of the appended phenolic units are remarkably more reactive than the sulfur atoms with antioriented aromatic subunits. Moreover, the most easily formed syn-oriented equatorial configuration is highly preferred over the corresponding axial arrangement which was never observed. As demonstrated by the resolution of racemic products, partial S-oxidation represents a very interesting tool to access novel inherently chiral building blocks based on thiacalix[4]arenes.
Israel Journal of Chemistry, 2001
A new synthetic strategy for the construction of an inherently chiral, sulfur-bridged calix[4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix[4]arene derivative of 1,3-alternate conformation: Tetra(carboxymethyl) ether of p-tert-butyltetrathiacalix[4]arene of 1,3-alternate conformation was converted to the tetra(l-menthoxycarbonylmethyl) ether (8). Oxidation of the tetra l-menthyl ester 8 by treatment with NaBO 3 (1.1 molar equiv.) afforded a pair of diastereomers of the monosulfinyl derivatives (9) in 58% yield, which were readily separable by silica-gel column chromatography. Removal of the l-menthyl moieties followed by methyl esterification gave enantiomerically pure samples of inherently chiral (-)-and (+)-monosulfinyltrithiacalix[4]arene derivatives ((-)-10 and (+)-10) in 62 and 56% yield, respectively.
Tetrahedron, 2001
Practical methods for the synthesis of sulfinyl-(5,6) and sulfonylcalix[4]arenes (7,8) were provided by the selective oxidation of thiacalix[4]arenes (3,4) with controlled amounts of an oxidant such as NaBO3 or hydrogen peroxide under mild conditions. The coordination ability of thiacalix[4]arene 4 and the sulfinyl and sulfonyl analogs (6,8) toward a wide variety of metal ions was investigated by solvent extraction and compared to that of the conventional methylene-bridged calix[4]arene 2. It was shown that the metal-ion selectivities of the sulfur-containing ligands 4, 6, and 8 were controlled by the oxidation state of the bridging sulfur moiety, which was best understood based on the hard and soft acid–base (HSAB) principle by assuming the critical role of the bridging groups in coordination to the metal center. Thus, 4 preferred soft metal ions by binding with S, while 8 did hard ones by ligating with sulfonyl O in addition to the adjacent two phenoxide oxygens, respectively. In good accordance with this hypothesis, 6 could bind to both hard and soft metal ions by using sulfinyl O and S, respectively. These made sharp contrast to the parent methylene-bridged 2, which could not essentially extract any metal ions at all, lacking lone pair electrons on the methylene bridge for coordination.The binding selectivity of thiacalix[4]arene (TCA) and the sulfinyl and sulfonyl analogs, prepared by the oxidation of TCA, toward metal ions depended upon the oxidation state of the bridging sulfur.
Stereoselective alkylation of thiacalix[4]arenes
A direct tetraalkylation of thiacalix[4]arenes using procedures well established in ÔclassicalÕ calixarene chemistry usually gives the 1,3-alternate conformers as the main product (n-PrI/K 2 CO 3 /acetone) while the cone conformers are obtained only in very poor yields (n-PrI/NaH/DMF). Surprisingly, the so far almost inaccessible cone conformers can be prepared in high yields using the two-step procedure: dialkylation-dialkylation, opening the way for their further utilisation in supramolecular chemistry.
Upper rim substituted thiacalix[4]arenes
Tetrahedron Letters, 2003
The synthesis and structure of new tetrahydroxythiacalix arenes, existing in the cone conformation and possessing reactive bromide, chloromethyl or diorganylphosphoryl groups on the upper rim of the macrocycle are described. The molecular structure of tetrakis(diisopropoxyphosphorylmethyl)thiacalix[4]arene was examined by X-ray crystallography.
Tetrahedron Letters, 1998
Thiacalix[4]arenes, in which the four methylene birdge of calix[4]arenes are replaced by sulfide linkages, were selectively oxidized to sulfinyl- or sulfonylcalix[4]arene under mild conditions with control of the stoichiometry of the oxidant. Solvent extraction of the transition and alkaline earth metal ions with these hosts showed that the metal binding ability was governed by the oxidation state of the sulfur functionalities.Thiacalix[4]arenes (2, 3) were selectively oxidized to sulfonylcalix[4]arenes (4, 5) or sulfinylcalix[4]arene (6) by controlling the stoichiometry of the oxidant, whose complexation ability to metal ions were studied by solvent extraction.
Monosubstituted lower rim thiacalix[4]arene derivatives
Tetrahedron Letters, 2012
A clean and partially green route to monoalkyled thiacalix[4]arenes has been demonstrated. We have discovered that tetraalkylammonium halide can cleave selectively one of the two aryl alkyl ethers of dialkylated para-tert-butylthiacalix[4]arenes. Thus, p-tert-butyl thiacalix[4]arenes differently monoalkyled at the lower rim with acetyl, propyl, and benzyl group were synthesized in good yield.
Thiacalix[4]arenes with Triple Bonds at the Lower Rim: Synthesis and Structure
Macroheterocycles, 2013
Reaction of thiacalixarenes with propargyl bromide in the presence of potassium or cesium carbonates leads mainly to mixture of the corresponding tetrasubstituted derivatives adopting 1,3-alternate and partial cone conformations. Sodium salts like carbonate and hydride are not effective as the base for the etherification of lower rim of thiacalix[4]arenes by propargyl bromide. It was established that propargyl derivatives of thiacalix[4]arenes are in conformational exchange between forms due rotation of one aryl ring.
Journal of Inclusion Phenomena and Macrocyclic Chemistry, 2007
The synthesis and X-ray structure investigation of the cone shaped monodecyloxythiacalix[4]arene, as well as the introduction of the reactive bromide or chloromethyl groups on it's upper rim are described. Preparation of the amphiphilic derivative of thiacalixarene bearing three hydrophilic diethoxyphosphoryl groups at the upper rim and lipophilic decyloxy group at the lower rim is presented.
Monocyanomethylated thiacalix[4]arenes: synthesis and lower rim modification
Arkivoc, 2008
The selective monocyanomethylation of p-R-thiacalix[4]arenes (R = H, tert-Bu) with chloroacetonitrile in the presence of Na 2 CO 3 in DMF is described. Monocyanomethylated p-tertbutylthiacalix[4]arene has been synthetically exploited in the Ritter reaction with 1-adamantanol for the transformation to the corresponding amide. A thiacalix[4]arene having mixed amide and ester functionalities at the lower rim was synthesized by alkylation of 25-N-(1adamantyl)carbamoylmethoxy-p-tert-butylthiacalix[4]arene with ethyl bromoacetate.