Stannoxane

Shanzer and Mayer-Shochet have utilized disubstituted stannoxanes as covalent templates for the formation of tetralactones. In this procedure, a dialkyl stannoxane is condensed with a glycol to form a cyclic-distannoxane as illustrated below. In a typical preparation, the distannoxane (i) was dissolved in CCI4 (ca. 0.04 At) at reflux and sebacoyl chloride (2 eq) was added dropwise at reflux. After heating for 20 h, the solution was concentrated to a solid. Chromatography afforded the tetralactone in 30% yield. ... 

Both allylstannane transmetalation and thermolysis of homoallyl stannoxanes have been used to prepare 2-butenyltin halides as (E)j(Z) mixtures44-45. The reaction between 2-butenyl-(tributyl)stannane and dibutyltin dichloride initially provides dibutyl(l-methyl-2-propenyl)tin chloride as the kinetic product by an SE2 process, but this isomerizes under the reaction conditions to give a mixture containing the (Z)- and (E)-2-butenyl isomers46. 

A number of mixed metalloxanes, R MOSnRrX (M = Hg, Tl, Si, Ge, or Pb), have similarly been synthesized from the stannoxanes (R2SnO) and the metal compounds R MX (250), and the borostannoxanes B(OSnRs)3 and (R0)2B0SnR20SnR20B(0R)2 have also been characterized (251, 252). 

Structural Details. For 1, the hexameric "drum" has idealized Sg molecular symmetry. The geometry of the stannoxane framework of the molecule consists of six-membered rings in a chair conformation. 

The reactions can be carried out under mild conditions in the presence of triethylamine or an inorganic base such as potassium carbonate,388 and under the latter conditions, the kinetic resolution of PhCH(OH)CH2CH2OH has been achieved using a chiral stannoxane based on 1,1 -binaphthyl. 

MacKnight and co-workers reported the preparation and polymerization of PET cyclics at about the same time [38,39], Polymerization to high Mw (Mn = 20 GOO-27 000) was achieved within 10-25 min at temperatures of 270-293 °C, using antimony oxide as the catalyst at 0.3 -1.0 %. Other catalysts were also investigated, including the cyclic stannoxanes reported earlier by Brunelle et al. [14], However, at the high temperatures required for PET polymerization, the tin catalysts proved to be unstable. 

Monoderivatives of symmetrical diols.2 One possible route to these derivatives is treatment of the diol with di-n-butyllin oxide to form a stannoxane, which is then allowed to react with 1 equivalent of an acid chloride or sulfonyl chloride (equation I). L nsymmetrical diesters can be obtained by consecutive reaction of the stannoxane wilh two different reagents. 

Macrocyclic tetralactones. A method for preparation of these lactones (2) uses a stannoxane (1) as a covalent template (equation I). Formation of dilactones is not observed. 

Although there are a variety of polymers in this category,69 71 most polymers with tin atoms in the chain backbone are represented by the stannoxane structure 7.11,... 

In the middle of the 20th century synthetic methods started to develop, and the properties926 were studied of metal-stannoxane monomers and polymers having a Sn—O—M group, where M = Ge, Pb, Ti, P, as well as their analogs, containing SnEM (E = S, Se, Te, NR) chains. 

Both cadmium and mercury compounds M[SnR3]2 (R = Me, Et, Pr, f-Bu, Ph) are oxidized by air to the related stannoxanes and MO (M = Cd) or M (M = Hg)239,241. Peroxides, e.g. Bz202, also perform similar oxidations to form M(OBz)2(M = Cd) and BzOSnR3365. Even the thermally stable complexes with bulky ligands (R = Me3SiCH2) are also oxidized333. 

The polymer-supported random stannol/stannoxane copolymer 94 was shown to catalyse the lactonisation of hydroxycarboxylic acids170. 

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