A SOLUTION AND SOLID-STATE CONFORMATION OF 2-DIPHENYLPHOSPHINOYL-1,3-DIOXANES - THE NATURE OF O-C-P ANOMERIC INTERACTIONS

Diastereoisomeric 2-diphenylphosphinoyl-1,3-dioxanes 1-4 were synthesized either via the Arbuzov reaction of isopropyl diphenylphosphinite with (1,3-dioxan-2-yl)trimethylammonium iodides or via the transacetalization reaction between 1,3-diols and diphenyl(diethoxymethyl)phosphine oxide. The latter reaction afforded less thermodynamically stable isomers of 3 and 4 in a good yield (44 and 56%, respectively). The magnitude of the anomeric effect in this system determined according to the Franck's equation was found to be 19.7 kJ/mol. Both the NMR and X-ray structural data concerning cis-4,6-dimethyl-1, 3-dioxane derivatives 4 suggest that the anomeric effect could stem from several interactions, including the n(o)-sigma*c-p negative hyperconjugation and intramolecular hydrogen bond formation.