Beta-halo-alpha,beta-unsaturated gamma-sultones.
The reaction of beta-iodo-alpha,beta-unsaturated gamma-sultones (i.e., 4-halo-1,2-oxathiole 2,2-dioxides) in aprotic polar solvents such as DMSO or acetone, with 'soft' nucleophiles such as iodide or thioacetate, yields an allenesulfonate by a very facile halophilic ring-opening E(2)-elimination. The 'harder' nucleophile, azide ion, reacts under the same conditions to yield the corresponding beta-azido-alpha,beta-unsaturated gamma-sultone (i.e., 4-azido-1,2-oxathiole 2,2-dioxide), displacing the beta-halide by an addition-elimination mechanism. In contrast, in the hydroxylic solvent CD(3)OD at ambient temperature, various nucleophiles yield neither of the above-mentioned products, but catalyze a rapid replacement of the Calpha-H by deuterium. Factors underlying this intriguing rapid exchange are proposed. Interestingly, the beta-bromo analogue exhibits similar reactivity except for the halophilic ring-opening. Calculations indicate the relative importance of the beta-halogen and the S-O(-C) bonds in enhancing the acidity of the H-C(alpha)S(O)2- grouping.
Department of Chemistry, Bar-Ilan University, Ramat-Gan 52900, Israel. bravers@mail.biu.ac.il
Samuel
S
Braverman
Tatiana
T
Pechenick-Azizi
Dan T
DT
Major
Milon
M
Sprecher