2-alkenyl-1,2,3-diazabora-5-cyclopentenes products of rearrangement reactions from lithiated ketazines and various halofunctional aryl-, amino- and aryloxyboranes

2-Alkenyl-1,2,3-diazabora-5-cyclopentenes are obtained from the dilithiated tert-butyl(trimethylsilylmethyl)ketazine 1 and BX3 (X = F, Cl): 2, 3 or fr om a variety of dilithiated ketazines and YBX2 (Y = (Pr2N)-N-t, C6H5, 2,4,6 -Bu-3(t)-C6H2, 2,6-Bu-2(t)-C6H3O; X = F, CI): 4 - 7, 9 - 12 or even with (E t2N)(2)BCl: 8. Due to their conjugated pi -system the title compounds are c olored (deep orange to bright yellow) and stabilized with respect to other expected products. If the lithiation cannot be achieved on the alpha -C-ato m bonded to the nitrogen-atom, lithium is coordinated to the azine N-atom(s ), Upon treatment with (Pr2NBF2)-N-t this leads to splitting of the N-N bon d of the ketazine and addition of the R2C=N-groups to boron as in 13 or to a borylation of one of the N-atoms as in 14 A C-borylated precursor, 15, wa s also isolated. The compounds were characterized by NMR: H-1, B-11, C-13, F-19, Si-29; by MS and C,H-elemental analyses. X-ray structure analyses are presented for 6 and 15.