Trimethyl borate assisted chemoselective synthesis 1,5-dihydrodiazepines from hemicurcuminoids and o-phenylenediamines

Abstract

In this work, we demonstrate the switchable transformation of hemicurcuminoids to 1,5-benzodiazepines or 1,5-dihydrobenzodiazepines. The synthesis of these compounds was based on the boron-activated addition of o-phenylenediamines to hemicurcuminoids in DCM. This convenient and simple protocol allows obtaining functionalized 1,5-dihydrobenzodiazepines with yields up to 65 %. The effect of boron activator was demonstrated. The use of acetic acid as a solvent changes the chemoselectivity of addition of o-phenylenediamine and 1,5-benzodiazepines are formed up to 40 % yield. Moreover, 1,5-dihydrobenzodiazepines undergoes recyclization into 1,5-benzodiazepines under acidic conditions.