A combined experimental and density functional study of 1-(arylsulfonyl)-2-R-4-chloro-2-butenes reactivity towards the allylic chlorine

Abstract

Nucleophilic substitution and dehydrochlorination reactions of a number of the ring-substituted 1-(arylsulfonyl)-2-R-4-chloro-2-butenes are studied both experimentally and theoretically. The developed synthetic procedures are characterized by a general rapidity, cheapness, and simplicity providing moderate to high yields of 1-arylsulfonyl 1,3-butadienes (48-95%), 1-(arylsulfonyl)-2-R-4-(N,N-dialkylamino)-2-butenes (31-53%), 1-(arylsulfonyl)-2-R-2-buten-4-ols (37-61%), and bis[4-(arylsulfonyl)-3-R-but-2-enyl]sulfides (40-70%). The density functional theory B3LYP/6-311++G(2d,2p) calculations of the intermediate allylic cations in acetone revealed their high stability occurring from a resonance stabilization and hyperconjugation by the SO 2 Ar group. The reactivity parameters estimated at the bond critical points of the diene/allylic moiety display a high correlation (R 2 > 0.97) with the Hammett (σ p ) constants. 1-Arylsulfonyl 1,3-butadienes are characterized by a partly broken π conjugated system, which follows from analysis of the two-centered delocalization (δ) and localization (λ) index values. The highest occupied molecular orbital energies of 1-arylsulfonyl 1,3-butadienes are lower than those of 1,3-butadiene explaining their low reactivity towards the Diels-Alder condensation.