Stannylene Acetals Research Articles

Substituted triethylene glycols from dibutylstannylene acetals

Stannylene acetals prepared from disubstituted vicinal diols can be alkylated with a half equivalent of 1,2-dibromoethane to produce tetrasubstituted triethylene glycols 2, or with two equivalents of 2-chloroethanol to produce disubstituted triethylene glycols 1.

Dibutylstannylene acetals: Useful intermediates for the regioselective sulfation of glycosides.

Sulfated mono- and disaccharides were synthesised by a novel sulfation method via regioselective activation of the saccharides to their dibutyltin stannylene acetals, followed by treatment with sulfur trioxidetrimethylamine. This methodology was applied to the synthesis of 3′-sulfated lactosides 15 and 23, galactosylceramide sulfatide 3 and 2′-sulfated maltosides 30, 32 and 34.

ChemInform Abstract: An Improved Method for the Regioselective Oxidation of Stannylene Acetals and Dimerization of the α‐Hydroxy Ketone Products.

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Regioselective Formation of Di-O-Benzyl-Substituted Hexopyranosides via Stannylene Acetal Intermediates

Abstract The reactions of dibutylstannylene acetals derived from several methyl hexopyranosides with benzyl bromide have been investigated. These reactions occur readily in benzyl bromide at 85 °C. At reaction times of one to two days, the major products are di-O-benzyl derivatives. In several cases, single di-O-benzyl derivatives are the predominant products: methyl α-D-glucopyranoside and methyl β-D-galactopyranoside gave the 2,6- and 3,6-di-O-benzyl ethers in 82 and 70% yields, respectively. The species present in these reactions and the reaction pathway are discussed.

Regioselective protection of threo-2,3-dihydroxybutanoic esters

Abstract Monoprotected derivatives of optically pure diolester 1 are regioselectively constructed by lipase-based methodologies as well as via the stannylene acetal of 1 .

An Improved Method for the Regioselective Oxidation of Stannylene Acetals and Dimerization of the α-Hydroxyketone Products

Abstract Dibutylstannylene acetals, particularly those derived from terminal diols, were found to be oxidized regiospeeifically to α-hydroxyketones in good to excellent yield by N-bromosuccinimide. One of the products, 3-deoxy-l,2-O-isopropylidene-α-D-erythro hexofuranos-5-ulose (8), exists to about 20% in solution as a mixture of dimers. One of the dimers can be obtained as a solid and its structure was determined tentatively by a combination of NMR experiments and MM3 molecular mechanics calculations.

The crystal structure of methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D- glucopyranoside

The determination of the crystal structure of methyl 4,6-O-benzylidene-2,3-O-dibutylstannylene-α-D-glucopyranoside (1) was repeated from data collected at −70 °C because the previous assignment had a large R value (10.9%) and because this structure was the key link in assignment of structures of all stannylene acetals in solution. Crystals of 1 are orthorhombic, of space group P212121, with a = 12.479(2), b = 19.202(5), c = 19.654(6) Å, Z = 4, R = 0.0597 (Rw = 0.0612) for 3623 independent reflections with I > 3σ(I). Compound 1 is a dimer linked together by a four-membered 1,3-dioxa-2,4-distannetane ring containing the O-3 atoms from the two glucose units. Deviations from C2 symmetry are much smaller than reported earlier and lie mainly in the orientations of the butyl groups. The butyl groups are still significantly disordered at −70 °C. It is suggested that steric effects of these flexible butyl groups may be an important factor in the selectivity for dicoordinate oxygens previously observed in reactions of stannylene acetal dimers with electrophiles.

Tin-119 NMR of 1,3,2-dioxastannolanes and a 1,3,2-dioxastannane in the solid state

The cross-polarized static and high-resolution magic angle spinning 119Sn NMR spectra of a number of 2,2-dialkyl-1,3,2-dioxastannolanes and one 1,3,2-dioxastannane have been measured in the solid state. For the four compounds on which X-ray studies had been performed, the numbers and positions of the isotropic peaks in the high-resolution spectra were related to the number of tin sites present and the state of oligomerization of the compounds. The chemical shifts of hexacoordinate Sn nuclei are 35–80 ppm larger in polymeric solids than for the same compounds in solution where the compounds exist as trimers and tetramers. States of oligomerization for solids that had not been previously studied by X-ray crystallography were determined using CP/MAS 119Sn NMR spectroscopy. The principal components of the 119Sn chemical shift tensors were obtained from the static spectra and used to calculate chemical shift anisotropies and asymmetry parameters. The values of the chemical shift anisotropies ranged from 600 to 800 ppm for 1,3,2-dioxastannolanes but the value for a 1,3,2-dioxastannane was larger, 919 ppm. The chemical shift anisotropies measured directly from the solid-state powder patterns are in excellent agreement with the values derived from previous variable temperature spin-lattice relaxation measurements in solution when the same oligomer was present in both states. Our results support our previous conclusion that the antisymmetric terms of the chemical shift tensor make a small or negligible contribution to the rate of 119Sn spin-lattice relaxation in these compounds. Keywords: 1,3,2-dioxastannolanes, stannylene acetals, 119Sn NMR, 119Sn NMR of solids, 119Sn chemical shift an-isotropy.

The structure of 2,2-dibutyl-1,3,2-dioxastannane in the solid state and in solution

Crystals of 2,2-dibutyl-1,3,2-dioxastannane (1) are orthorhombic, of space group Pnma, with a = 7.663(3), b = 18.437(2), c = 9.277(4) Å, Z = 4, R = 0.0568 (Rw = 0.0551) for 1183 independent reflections with I > 3σ(I). Compound 1 is a polymer in which each monomer unit is joined to the next by a four-membered (SnO)2 ring. The Sn—O bond lengths inside the monomer units average 2.04 Å while those between monomers average 2.57 Å. The mirror plane of the crystal contains the atoms in the four-membered rings and the other oxygen atoms. Two of the three remaining carbon atoms in the six-membered rings of the monomer units are close to the mirror plane. The other carbon atom is disordered above and below the plane. It was shown by 119Sn NMR spectroscopy that solutions of 1 contain mixtures of oligomers that consist mainly of dimers, trimers, and tetramers in chloroform-d. ΔG0 values for dimmer–trimer equilibria and dimmer–tetramer equilibria of −2.5 and −1.5 kcal mol−1 were obtained from integration of low temperature 119Sn NMR spectra. These values favour the higher oligomers slightly less than those for 2,2-dibutyl-1,3,2-dioxastannolane. Keywords: 1,3,2-dioxastannanes, stannylene acetals. X-ray crystallography, 119Sn NMR spectroscopy.

NMR relaxation of tin-119 in pentacoordinate and hexacoordinate environments

Carbon-13 and 119Sn nuclear magnetic resonance spin-lattice relaxation times at 8.48 T and at 4.70 T have been measured at several temperatures for a number of 2,2-di-n-butyl-1,3,2-dioxastannolane derivatives, most of which were prepared from monosaccharide derived diols. The tin nuclei in these compounds, which are at either pentacoordinate or hexacoordinate sites, have 119Sn T1values that are relatively short, between 13 ms and 300 ms. At 8.48 T, chemical shift anisotropy is the only important mechanism for relaxation of the 119Sn nuclei in these compounds. However, at 4.70 T, the 1H,119Sn dipole–dipole mechanism also contributes slightly. The principal components of the 119Sn chemical shift tensor for the pentacoordinate site in the dimeric structure of methyl 4,6-O-benzylidene-2,3-dibutylstannylene-α-D-glucopyranoside (1) were determined directly from the static 119Sn spectrum of a powdered sample and indirectly from slow spinning CP/MAS spectra using both the Herzfeld–Berger procedure and computer simulation. The tin shift tensor for 1 in the solid state is non-axially symmetric with η = 0.49 ± 0.03. The chemical shift anisotropy determined from the solid state experiments, 748 ± 20 ppm, was in good agreement with the value obtained from the solution T1data, 720 ± 50 ppm. For compounds containing both pentacoordinate and hexacoordinate tin atoms, the 119Sn relaxation data indicate that the tin chemical shift anisotropies for the hexacoordinate sites are approximately 1.6 times those of the pentacoordinate sites. Keywords: 119Sn NMR, NMR relaxation, stannylene acetals, 1,3,2-dioxastannolanes.

The structures and reactions of stannylene acetals from carbohydrate-derived trans-diols. Part I. In the absence of added nucleophiles

Di-n-butylstannylene acetals of benzyl 4,6-O-benzylidene-α- and -β-D-glucopyranoside and galactopyranoside have been prepared and studied in solution by 1H, 13C, and 119Sn nuclear magnetic resonance spectroscopy. The species present in solution have been identified from the 119Sn nmr spectral data, by comparison of the 13C nmr chemical shifts of the stannylene acetals and their precursor diols and also by analysis of the products of reactions performed without added nucleophiles. The orientations of the two substituents on the carbons in the pyranose ring attached to the carbons in the stannylene ring determine the structures adopted by the stannylene acetal in solution. If one substituent is axial and the other equatorial, the stannylene acetal exists as a single symmetrical dimer in which the two oxygen atoms in the two 1,3,2-dioxastannolane rings adjacent to the axial substituents are dicoordinate. A stannylene acetal with two adjacent equatorial substituents exists as a non-interconverting mixture of dimers; one with two adjacent axial substituents is present as a rapidly interconverting mixture of dimers, trimers, and tetramers. Benzoylation and benzylation of the latter two types of stannylene acetals have been performed and have been shown to be only slightly regioselective in contrast to the known highly regioselective reactions of the first type. Only when single dimers are present are regiospecific or highly regioselective reactions obtained. The causes of the variation in the species present and of the reaction regioselectivity for different stannylene acetals are discussed. Keywords: stannylene acetals, 1,3,2-dioxastannolanes, 119Sn NMR spectroscopy, regioselective reactions, carbohydrates.

ChemInform Abstract: Regioselective Alkylation and Acylation of Methyl 2,6‐Dideoxyhexopyranosides via Their Stannylene Acetals: Key Step for the Synthesis of Daunosamine and Related Amino Sugars.

AbstractThe L‐lyxo‐hexopyranoside (III) is converted into the benzyl ether (I) and the tosylate (V).

Regioselective Alkylation and Acylation of Methyl, 2,6-Dideoxyhexo-Pyranosides Via Their Stannylene Acetals: Key Step for the Synthesis of Daunosamine and Related Amino-Sugars

Abstract Synthetic intermediates for the preparation of 3-amino-2,3,6 (or 4-amino-2,4,6)-trideoxy-L-hexopyranosides, sugar moieties of anthracycline antibiotics, were selectively obtained from stannylene acetals of methyl 2,6-dideoxy-α-L-lyxo and arabino-hexopyranosides.