Reactivity of C,N-chelated organoboron compounds with lithium anilides--formation of unexpected 1,2,3-trisubstituted 1H-2,1-benzazaboroles.
A set of C,N-intramolecularly coordinated boranes containing various C,N-chelating ligands L(1-3) (where L(1) = [o-(CH=NtBu)C6H4], L(2) = [o-(CH=N-2,6-iPr2C6H3)C6H4], L(3) = [o-(CH2NMe2)C6H4]); L(1-3)BCl2 (for 1 L = L(1), for 2 L = L(2), for 5 L = L(3)), L(1)BPhCl (3) and L(1)BCy2 (4) (where Cy = cyclohexyl) were synthesized and fully characterized by multinuclear NMR spectroscopy and in cases of 1 and 3-5 by the single crystal X-ray diffraction analysis. The reaction of with the anilides ArNHLi (Ar = 2,6-Me2C6H3 or 2,6-iPr2C6H3) proceeded via unexpected addition of anilide across the C=N bond yielding 1,2,3-trisubstituted 1H-2,1-benzazaboroles 6-11, whose structures were unambiguously established by single crystal X-ray diffraction analysis (except for 11) and multinuclear NMR spectroscopy. In contrast, compounds 4 and 5 were inert towards ArNHLi. The investigation dealing with the reaction mechanism between the parent boranes 1-3 and ArNHLi revealed that amidolithiation of the C=N double bond involved in the ligand backbones is the crucial step of the whole reaction. The C=N double bond in 1-3 is activated by its coordination to the ortho bonded Lewis acidic boron center, which was also proven by the fact that the non-substituted ligand L(1)H did not react with ArNHLi under the same reaction conditions in an analogous reaction.
Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Pardubice, Czech Republic.
Martin
M
Hejda
Antonín
A
Lyčka
Roman
R
Jambor
Aleš
A
Růžička
Libor
L
Dostál