Synthetic applications of cyclic α-chloro-ethers and -thioethers. Part 5. Tetrahydrofuranyluracil derivatives: conformational properties in solution

Abstract

With the aid of high-frequency n.m.r. spectroscopy (360 MHz) and computer simulation all chemical shift and coupling constant parameters of tetrahydrofuranyluracil derivatives (3a and b) and (4a and b) have been obtained. By comparison with model compounds (1) and (2) and with literature studies of (deoxy)ribonucleosides a conformational analysis of (3a and b) and (4a and b) has been carried out. Vicinal coupling constants between THF protons are consistent with an N⇌S conformational equilibrium, the former being preferred in (3a and b) and the latter in (4a and b). Finally, the relative orientation of THF and uracil rings in (3a and b) is described.