COMPARISON OF GAS-PHASE AND CONDENSED-PHASE S(N)I REACTIONS - THE COMPETITIVE 4-AND 5-CENTER CYCLIZATIONS OF THE 3,4-EPOXYBUTOXIDE ANION - A JOINT EXPERIMENTAL AND THEORETICAL-STUDY

Ab initio calculations [at the MP2-Fc/6-31+G(d) level] indicate that t he 3,4-epoxybutoxide anion should undergo competitive S(N)i cyclisatio ns (through four- and five-membered transition states) to yield the (M -H)(-) ions of oxetan-2-ylmethanol and tetrahydrofuran-3-ol respective ly. The barriers to the transition states are comparable (ca. 70kJ mol (-1)) for each process, and the latter product is the more stable by 8 2 kJ mol(-1) at the level of theory indicated. Gas phase studies of th e 3,4-epoxybutoxide anion excited by collisional activation are in acc ord with this scenario, and sho, in addition, that deprotonated 2-oxet anylmethanol can convert to the starting materioa. Base treatment of 2 -(oxiran-2-yl)ethan-1-ol (3,4-epoxybutan-1-ol) in two different solven t systems [10% aqueous sodium hydroxide and sodium hydride-tetrahydrof uran (both at reflux)] yields the same two products observed in the ga s phase studies. However, deprotonated tetrahydrofuran-3-ol is the kin etic product in both solvent systems.