Reactivity of Carbon Acids toward 4,6-Dinitrobenzofuroxan. Studies of Keto-Enol Equilibria and Diastereoisomerism in Carbon-Bonded Anionic ? Complexes

Article abstract of DOI:10.1021/jo00330a033

4,6-Dinitrobenzofuroxan (DNBF) reacts with monoketones and β-diketones in dimethyl sulfoxide solution to give carbon-bonded ? adducts.As shown by NMR, the reactions occur in the absence of any added base, emphasizing the highly electrophilic character of this heterocycle.With monoketones only ketonic adducts are formed, while with β-diketones both enolic and/or ketonic ? complexes are observed.The presence of two chiral centers in the DNBF-cyclopentanone adduct enabled the first characterization of two diastereomeric ? complexes.The structure of both kinetically and thermodynamically favored diastereomers are tentatively assigned on the basis of the geometry of the transition states leading to them.It is also shown that enolic ? adducts are formed from the reaction of 1,3,5-trinitrobenzene with β-diketones in the presence of base.