Nitronate anion recognition and modulation of ambident reactivity by hydrogen-bonding receptors

Nitronate anions were shown to form complexes in DMSO with hydrogen-bonding receptors such as 1,3-dimethylthiourea 1 (K-a = 120 M-1) and bicyclic guan idinium 2 (K-a = 3200 M-1). A ditopic bis-thiourea exhibited increased asso ciation with substrates, that contained either two nitronates (K-a = 7000 M -1) or a combination of nitronate and carboxylate (K-a = 7200 M-1). Complex ation of nitronate resulted in a change in the ambident reactivity during a lkylation with p-nitrobenzyl bromide. The predominant reaction pathway was shifted from oxygen alkylation to carbon alkylation as receptor binding str ength increased. Kinetic analysis indicated an overall inhibition of nitron ate reactivity, and this suggests that greater suppression of the oxygen pa thway allows carbon alkylation to predominate.