Generation of 1, 2-azaboretidines via reduction of ADC borane adducts. Issue 6 (24th April 2015) - Braunschweig, H.
Abstract : ADC borane adducts RBX2 ·ADC (R = Mes, Dur; X = Cl, Br; ADC = :C(NiPr2 )2 ) have been prepared and reduced by KC8 to afford air stable 1, 2-azaboretidines with high selectivity. Abstract : Reaction of the acyclic (diamino)carbene (ADC) :C(NiPr2 )2 (1 ) with different dihaloboranes of the type RBX2 (R = Mes, Dur; X = Cl, Br) smoothly afforded a novel class of ADC-stabilized borane adducts. For MesBBr2 however, the reaction did not stop at the adduct level, but an uncommon rearrangement process occurred, which eventually resulted in the formation of a 5-membered boracycle after elimination of mesitylene. Chemical reduction of the ADC borane adducts by KC8 selectively yielded air stable 1, 2-azaboretidines. Detailed DFT studies suggest a reduction mechanism involving a highly reactive borylene intermediate, which is converted into the boracycles via a rearrangement/C–H activation sequence.