This paper is dedicated to Professor Arthur S. Perlin on the occasion of his 67th birthday T. BRUCE GRINDLEY and RASIAH THANGARASA. Can. J. Chem. 68, 1007 (1990). Di-n-butylstannylene acetals of benzyl 4,6-0-benzylidene-a-and -P-D-glucopyranoside and galactopyranoside have been prepared did studied in solution by 'H, I3c, and nuclear magnetic resonance spectroscopy. The species present in solution have been identified from the '19sn nrnr spectral data, by comparison of the l3C 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.Key words: stannylene acetals, 1,3,2-dioxastannolanes, IL9sn NMR spectroscopy, regioselective reactions, carbohydrates.T. BRUCE GRINDLEY et RASIAH THANGARASA. Can. J. Chem. 68, 1007 (1990). On a prtpart les di-n-butylstannylkne acttals des 4,6-0-benzylidene-a-et -P-glucopyranosides et galactopyranosides de benzyle et on les a ttudits, en solution, en faisant appel h la rtsonance magnttique nucltaire du IH, du 13C et du 119Sn. On a identifit les espkces prtsentes en solution h partir des donntes de la rmn du Il9Sn, par comparaison des dtplacements chimiques en rmn du 13C des stannylkne acttals et des diols qui leur ont donnt naissance ainsi que parune analyse des produits des rtactions rtalistes en l'absence de nucltophiles. Les orientations des deux substituants attachts aux carbones du cycle pyranosique qui font partie du cycle stannylkne dtterminent les structures adopttes par le stannylkne acttal en solution. Si l'un des substituants est axial alors que I'autre est tquatorial, le stannylene acttal existe sous la forme d'un dimkre symttrique unique dans lequel les deux atomes d'oxygkne des deux cycles 1,3,2-dioxastannolanes adjacents aux substituants axiaux sont doublement coordonnts. Un stannylkne acCtal comportant deux substituants tquatoriaux adjacents existe sous la forme...

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. J. Chem. 68, 2102 (1990).Carbon-13 and "' Sn 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-l,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 "'~n TI values 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 "' Sn nuclei in these compounds. However, at 4.70 T, the 'H,"'S~ dipole-dipole mechanism also contributes slightly. The principal components of the '19Sn chemical shift tensor for the pentacoordinate site in the dimeric structure of methyl 4,6-0-benzylidene-2,3-dibutylstannylene--~-glucopyranoside (1) were determined directly from the static lI9sn 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 q = 0.49 k 0.03.

The cross-polarized static and high-resolution magic angle spinning ""n 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 pprn 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 'I9Sn NMR spectroscopy. The principal components of the 119 Sn 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 pprn 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 '19sn spin-lattice relaxation in these compounds.Key words: 1,3,2-dioxastannolanes, stannylene acetals, 'I9Sn NMR, '"Sn NMR of solids, '"Sn chemical shift anisotropy. Pour les quatre composCs pour lesquels on a determint des structures par diffraction des rayons-X, on a pu relie les nombres et les positions des pics isotropes dans les spectres haute resolution avec le nombre des sites d'Ctain presents et 1'Ctat d'oligomerisation des composCs. Les dCplacements chimiques des noyaux de Sn hexacoordonnCs sont de 35 80 pprn plus grands dans les polymkres solides que dans les m&mes composCs en solution alors que les composes existent sous la forme de trimkres ou de tktramkres. Faisant appel a la RMN du 'I9sn par CP/MAS, on a determink les Ctats d'oligomkrisation des solides que I'on n'avait pas CtudiCs anterieurement par diffraction des rayons-X. En se basant sur les spectres statiques, on a obtenu les principales composantes des tenseurs des deplacements chimiques du 'I9Sn et on les a utilisees pour calculer les anisotropies des dCplacements chimiques et les parametres dlasymCtrie. Pour les 1,3,2-dioxastannolanes, les valeurs des anisotropies des deplacements chimiques varient de 600 a 800 ppm; toutefois, pour un 1,3,2-dioxastannane, cette anisotropie est plus ClevCe, soit 919 ppm. Lorsque le m&me oligomere est present dans les deux Ctats, les anisotropies des deplacements chimiques mesures directement a partir des patrons de poudres a 1'Ctat solide sont en tres bon accord avec les valeurs obtenues ...

Can. J. Chem. 70, 197 ( 1 992).Crystals of 2,2-dibutylil,3,2-dioxastannane (I) are orthorhombic, of space group Pnma, with a = 7.663(3), b = 18.437(2), c = 9.277(4) A, Z = 4, R = 0.0568 (R,,. = 0.0551) for 1183 independent reflections with I > 3u(I). Compound 1 is a polymer in which each monomer unit i : joined to the next by a four-membered (SnOI? ring. The Sn-0 bond lengths inside the monomer units average 2.04 A while those between monomers average 2.57 A. 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 "'Sn NMR spectroscopy that solutions of 1 contain mixtures of oligomers that consist mainly of dimers, trimers, and tetramers in chloroform-d. AGO values for dimer-trimer equilibria and dimer-tetramer equilibria of -2.5 and -1.5 kcal mol-' were obtained from integration of low temperature " 9~n NMR spectra. These values favour the higher oligomers slightly less than those for 2,2-dibutyl-1,3,2-dioxastannolane.Key words: 1,3,2-dioxastannanes, stannylene acetals, X-ray crystallography, 'I9sn NMR spectroscopy. Le compose 1 est un polymkre dans lequel chaque unit6 de monomere est like a la suivante par un cycle aoquatre chainons (SnO),. La longueur moyenne des liaisons Sn-0 a l'intkrieur des unites de monomkre est tgale a 2,04 A alors que celle observke entre les monomkres est de 2,57 A. Le plan miroir du cristal contient les atomes des cycles a quatre chainons ainsi que les autres atomes d'oxygtne. Deux des trois autres atomes de carbone des cycles a six chainons des unites de monom6re se trouvent pres du plan miroir. L'autre atome de carbone est dCsordonnC au-dessus et au-dessous du plan.