Synthesis, structure, and thermolysis of a pentacoordinate 1,2-oxastibetane

Isomeric pentacoordinate 1,2-oxastibetanes bearing the Martin ligand have been synthesized by the reactions of bromo(2-hydroxyalkyl)stiboranes with sodium hydride of which one of the isomers was characterized by X-ray crystallographic analysis and NMR spectroscopy. Thermolysis of the isomer shown (CD3CN, 140 degrees C) afforded the oxirane with retention of configuration, while its thermolyses in the presence of lithium bromide and LiBPh4.3DME provided the oxirane with inversion of configuration and the olefin. The addition of the salts in the thermolyses of this pentacoordinate 1,2-oxastibetane controls both the stereochemistry of the oxirane formed and the ratios of the three main products.