2-DIPHENYLARSINO-DERIVATIVE, 2-DIPHENYLPHOSPHINYL-DERIVATIVE, AND 2-TRIPHENYLSTANNYL-DERIVATIVE OF METHYL 4,6-O-BENZYLIDENE-2-DEOXY-ALPHA-D-ALTROPYRANOSIDE - CRYSTAL-STRUCTURE OF THE PHOSPHINYL DERIVATIVE

Reaction of methyl 2,3-anhydro-4,6-O-benzylidene-alpha-D-allopyranoside (3) with Ph(n)MLi [M = As or P, n = 2; M = Sn, n = 3] gives methyl 4,6-O-benzylidene-2-deoxy-2-M-alpha-D-altropyranoside (4, M = Ph(2)As, Ph(2)P or Ph(3)Sn). Compound (4, M = Ph(2)P) is readily oxidised in air to the phosphinyl derivative (4, M = Ph(2)P(O)). Characterisation of (4, M = Ph(2)As, Ph(2)P(O), or Ph(3)Sn) was achieved by NMR spectroscopy, including solid state NMR spectroscopy, for (4, M = Ph(2)As) and (4, M = Ph(3)sn), and by X-ray crystallography for [4, M = Ph(2)P(O)]. In the solid state both the benzylidene and pyranose rings in [4, Ph(2)P(O)], adopt chair conformations. The pentavalent phosphorus atom has a distorted tetrahedral geometry with C-P-C valency angles in the narrow range from 105.7(3) to 106.0(3)degrees and the C-P-O valency angles ranging from 111.3(3) to 115.6(2)degrees; the P-C-aryl bond lengths are 1.808(5) and 1.815(6) Angstrom, while the P-C-alkyl bond length is slightly larger, being 1.829(6) Angstrom. Intermolecular H-bonding, involving HO and O(P) centres, links the molecules in the crystal.