1.3.2- Dioxastannolanes

The enantiomeric allylic stannanes in Equations (111) and (112) show only the H-ene reaction, and proceed with complete stereoselectivity. The former compound gives also some dioxastannolane, and if an electron-donating group is present, this dioxastannolane can be the only product (Equation (113)).2... 

The 1,3,2-dioxastannolanes are important in organic synthesis because they can readily be derived from dialkyltin oxide and 1,2-diols, as in carbohydrates the reaction can be carried out in toluene in a few minutes under microwave irradiation.387 The dioxastannolanes can then be subjected to regioselective reaction with an electrophile such as an acyl chloride (Equation (140)) or sulfonyl chloride, or an isocyanate. The acylation or sulfonation can be carried out with catalytic amounts of the dialkyltin oxide, including the recoverable (C6F13CH2CH2)2Sn0.388... 

Factors that determine the regioselectivity are the deactivation of one of the two oxygen nucleophiles by stereochemically controlled dimerization of the dioxastannolane, and by equilibration of the possible isomeric products (Equation (141)).389-391... 

An improved route to the dihydrides is the reduction of the dioxastannolanes (see above) with THF BH3. The byproducts are easily removed by washing with water, and yields are very good (Equation (143)).395... 

Many of the tin heterocycles have been characterized by Mossbauer spectra. Among these the complexes formed by 2,2-dibutyl-l,3,2-dioxastannolane and its methyl-substituted derivatives with pyridine, DMSO, DMF, sulfolane and THE <83JOM(258)7> and fused benzo-1,3,2-dithiastannolanes <85JOM(290)4l> should be mentioned. 

Coordination and self-association in the solid and in solutions of 1,3,2-dioxastannolanes and related compounds (see Section 4.24.2.3) can be regarded as the result of nucleophilic attack at... 

Tin glycolates or o-diphenolates undergo photochemical or thermal radical cyclization (Equation (31)) to 1,3,2-dioxastannolanes or benzo-l,3,2-dioxastannolenes in high yields <86JOM(303)87>. 

In contrast to their germanium analogues, the main applications of tin heterocycles are not concerned with their biological activity although several 1,3,2-dioxastannolane derivatives exhibit in vitro antitumor activity (88BSB873, 92H(34)549>. The two most important fields involve technical uses of 1,3,2-diheterastannolanes and their use in organic synthesis. 

Regioselective oxidation by brominolysis of dioxastannolane obtained from methyl / -L-ara-binopyranoside made it possible to accomplish (after subsequent oximation and reduction) a facile synthesis of 4-amino-4-deoxy-L-arabinose, an amino-sugar found in lipopolysaccharides of some Salmonella R. mutant strains <83CPB3778>. 

Some chiral 1,3,2-dioxastannolanes were used as catalysts in asymmetric Diels-Alder reactions of cyclopentadiene with methyl acrylate <90JCR(S)278>. A-Alkenyl- and -cycloalkenyl 1,3,2-oxaza-stannolanes, generated in situ from chiral amino alcohols, gave optically active 2-substituted aldehydes and ketones in modest to high chemical and optical yields after alkylation with methyl acrylate or acrylonitrile (which is usual for enamines) and subsequent hydrolysis <85CC504,85JOC3863>. 

Simple organotin alkoxides as well as the cyclic dioxastannolanes are also suggested to associate in solution and in the solid state83,214. The degree of association depends on... 

Dibutyl-1,3,2-dioxastannolanes 19-21127, including two enantiomeric pairs, were tested in vitro on a variety of human tumor cell lines (HeLa, MM96L, MM418c5, C180-13S). There is no significant difference in cytotoxicity of optical isomers 19 and 20 or between compounds 19-22 and dibutyltin dichloride towards HeLa cells (ID37 = 0.2-0.5 pM). This lack of difference is consistent with hydrolysis to a common cytotoxic Bu2Sn2+ species. 

There have been numerous studies of 1,3-dioxastannolanes and related 1,3-thia or mixed 1,3-oxathia analogs, largely stemming from their syn-... 

The reaction chemistry of the 1,3,2-dioxastannolanes is vast and has been put to great use in various aspects of organic chemistry. Diorganotin derivatives of carbohydrates incorporate the dioxastannolane ring, and the structures of two such derivatives have already been commented on. The synthetic applications of intermediates of this type have been reviewed elsewhere (214-216) and are not discussed further. Substitution reactions have also proved useful synthetically, for example, in the formation of cyclic tetralactones [Eq. (52)] and urethanes (217-219), a subject which has also been reviewed (220). Two other substitution reactions using electrophilic carbon are shown in Eqs. (53) and (54), which typify several others of the same type (221,222). 

A,A-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO), will form complexes with the tin, breaking the polymeric structure of the dioxastannolane but maintaining a coordination number of greater than four at the metal. A m-R2Sn02L structure has been proposed on the basis of 119Sn chemical shifts (—137 to —189 ppm) and Mbssbauer data (A 2.11-2.82 mm/second). The donor ligand is readily lost under reduced pressure (224). 

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