Template Effect of Distannoxanes and Their Synthetic Applications

Abstract

Novel template effects of 1, 3-disubstituted 1, 1, 3, 3-tetraalkyldistannoxanes and their synthetic applications are summarized. The distannoxanes have a unique dimeric ladder structure induced by coordination of oxygen or hetroatoms to tins in the other chain. The bridging groups in the terminal positions are highly activated and thus easily substituted by an alkoxyl group. The tin atoms bonded to these electronegative groups are acidic enough to undergo coordination by one more carbonyl oxygen. Despite involving a metalloxane core, the distannoxanes are quite soluble in organic solvents. This is attributable to the doublelayered structure of the distannoxanes in which the surface alkyl groups prevent the inorganic core from being exposed to the solvent phase. These characteristic features lead to facile and selective chemical transformations of carbonyl compounds. Following to elucidation of the catalytic mechanism in urethane formation, distannoxane catalyzed transesterification is described wherein synthetiC usefulness and unusual solvent effect are revealed. The distannoxanes catalyze irreversible esterification reaction, the irreversibility arising from the doublelayered structure. Acetalization of carbonyls is also effected where unique transcarbonylation is involved. Finally, synthetically useful deacetalization and desilylation are described.