Collect. Czech. Chem. Commun. 2002, 67, 1084-1094

The Structural Basis for Hydrolysis Resistance in the Esters of (2-Formylphenyl)boronic Acid 2,4-Dinitrophenylhydrazones

Michael P. Groziaka,* and Paul D. Robinsonb

a SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025-3493, U.S.A.
b Department of Geology, Southern Illinois University, Carbondale, IL 62901-4324, U.S.A.


Under conditions that typically afford bicyclic boron heterocycles directly, (2-formylphenyl)boronic acids react with 2,4-dinitrophenylhydrazine in ethanol to give highly waterresistant diethyl boronate esters. Two such 2,4-dinitrophenylhydrazones were prepared and their X-ray crystal structures determined. Contrary to a previous suggestion that their unusual stability is due to an intramolecular N→B coordination giving a six-membered BN2C3 ring system based on a (Z)-hydrazone, these compounds instead were found to be (E)-hydrazones internally stabilized by a weak intramolecular interaction between nitrogen and boron from within a five-membered ring. Further study revealed that the electron deficiency of the starting hydrazine reagent plays a key role in determining the structure of the hydrazone isolated, and that the water-resistant boronate esters can be hydrolyzed under forcing conditions to the boronic acids.

Keywords: Boron; Boraheterocycles; Heterocycles; Hydrazones; Cyclizations; Crystal structure determination; Steroid analogues; Estrogen mimics.

References: 17 live references.