N-Methylpicramide–methoxide ion interactions: proton abstraction versus σ-complex formation

Abstract

The interactions of N-methylpicramide (NMP) with methoxide ion in dimethylsulfoxide–methanol media and with 1,4-diazabicyclooctane in dimethylsulfoxide have been investigated spectrophotometrically at 25.0 °C. Dimethylsulfoxide has been found to stabilize the conjugate base of NMP, formed via loss of hydrogen ion from the methylamino group, with respect to the anionic σ-complex generated via addition of methoxide ion to a ring carbon position. As a result, methanol–dimethylsulfoxide solutions rich in dimethylsulfoxide (i.e., 95/5, v/v, DMSO/MeOH) contain the conjugate base of NMP as the sole product of the 1:1 interaction of NMP and methoxide ion. At mole ratios of methoxide ion to NMP > 1 a second interaction results, yielding a dianion formed via addition of methoxide ion to one of the H-bearing ring carbon atoms of the conjugate base. Values of absorption maxima and molar absorptivities at the absorption maxima for the conjugate base of NMP and the dianion are reported here for the first time.