ANOMERIC AND STERIC EFFECTS OF BROMINE, CHLORINE AND METHOXY-GROUP IN CONFORMATIONAL ANALYSIS AND ANOMERIZATION OF HINDERED TETRAHYDROFURANS

Article abstract of DOI:10.1016/S0040-4020(01)87762-0

The NMR spectra of a series of hindered tetrahydrofuran compounds, disubstituted in C5 and with two polar groups in C2 (Br, Cl or Me in the anomeric position) and C3 (Br or Cl) have been examined.When the two polar groups are cis, the anomeric group is always in the axial orientation.If they are trans, three cases are observed.The molecule may be in a pure anomeric conformation, in a pure contra-anomeric conformation or is a mixture of the two.The anomerization reaction shows that the trans-isomers which are in the anomeric conformation appear more stable than the cis ones (> 1.5 kcal/mole).In the reverse case, the cis-isomer is slightly more stable (< 0.5 kcal/mole).Despite the difference of bulkiness, the tendency of the halogen substituents Cl and Br to be axial in C2 is greater than for the MeO group.