Structure characterization of the products of the reaction between racemic 1,2,4-butane triol and di-tert-butyltin oxide

Abstract

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, 1 and 2. Compound 1, which cannot be isolated as a pure product, was characterized in situ in C6D6 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 2, 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 Sn2O2 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 C6D6 solution structure of compound 2 is identical to that of the crystalline state, even though evidence is found for 2 to exist in solution as a mixture of 2-RS and 2-RR/SS dimers.