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Measurements of rate constants and substituent effects for three important elementary steps of proton-transfer reactions of phenylnitromethane were reported. The Hammett ρ values for the deprotonation of ArCH2NO2 with OH-, protonation of ArCH-NO2- with H2O, and protonation of ArCH-NO2- with HCl were determined in aqueous MeOH at 25 °C. Comparison of these experimentally observed ρ values with those calculated at B3LYP/6-31G* revealed that aci-nitro species (ArCH-NO2H), which is formed on the O-protonation of ArCH-NO2-, does not lie on the main route of the proton-transfer reaction. Analysis of the Brønsted plot implies that the proton-transfer reaction of most XC6H4CH2NO2 exhibits nitroalkane anomaly, but not for p-NO2C6H4CH2NO2, and that the transition state charge imbalance is an origin of anomaly. [ABSTRACT FROM AUTHOR]

The highly syn-diastereo- and enantioselective direct vinylogous Michael addition of α-thio substituted furanones with conjugate nitroalkenes was demonstrated using an axially chiral guanidine base catalyst. The method provides facile access to enantioenriched α,γ-functionalized butenolides that can be further manipulated, thereby rendering them useful synthetic intermediates., (© 2011 American Chemical Society)