Structure Characterization of the Products of the Reaction between Racemic 1,2,4-Butane Triol and Di-tert-butyltin Oxide

The reaction of di-tert-butyltin oxide with racemic 1,2,4-butane triol, aiming at synthesizing a model compound mimicking the tetra-tert-butyldistannoxane derivative of erythromycine A, affords two novel compounds, <BO>1</BO> and <BO>2</BO>. Compound <BO>1</BO>, which cannot be isolated as a pure product, was characterized in situ in C<INF>6</INF>D<INF>6</INF> solution by two-dimensional, multinuclear (¹H, ¹³C, ^119/117Sn) NMR and proven to exhibit the same structural organooxotin moiety as the tetra-tert-butyldistannoxane derivative of erythromycine A, with however the position of an exchangeable hydroxylic proton now being unambiguously defined. Compound <BO>2</BO>, isolated as a crystalline product, was characterized by X-ray diffraction analysis as the RS-isomer of a dimer generated from two monomeric units of opposite chirality obtained from 1:1 condensation of di-tert-butyltin oxide with racemic 1,2,4-butane triol; the hydroxylic protons of the OH groups of its carbon atoms C(1) and C(2) have been eliminated, giving rise to a five-membered cyclic 1,3,2 dioxastannolane-like pattern, where the oxygen of carbon C(1) of the ligand complexes the tin atom of a neighboring molecule, resulting in a centrosymmetric Sn<INF>2</INF>O<INF>2</INF> core; the hydroxylic proton of the OH group of carbon atom C(4) of the ligand forms an intramolecular hydrogen bridge with the oxygen atom of C(2). The C<INF>6</INF>D<INF>6</INF> solution structure of compound <BO>2</BO> is identical to that of the crystalline state, even though evidence is found for <BO>2</BO> to exist in solution as a mixture of <BO>2</BO>-RS and<BO> 2</BO>-RR/SS dimers.