(Iminoboryl)borates [R3B-B=NR]-: Rearrangement to (aminoboryl)boranes R2B-BR=NRE by the addition of electrophiles E

Article abstract of DOI:10.1002/cber.19961290318

(Iminoboryl)borates [Li(tmeda)₂][R₂R′B-B≡NR] (2a-c, R′ = Me, Me₃SiCH₂, Me₃CCH₂) are formed from the azadiboriridine NB₂R₃ (1, R = tBu) and LiR′ in the presence of tmeda. Vinyllithium brings about a ring expansion of 1 to give the five-membered anionic ring [-CH=CH-BR=NR-BHR-]^-, to which [Li(tmeda)]⁺ is bound (3). The (aminoboryl)boranes R₂B-BMe=NER (4a-c, EX = HCl, Mel, Me₃SiI) are obtained, when the polar compounds EX are added to 2a, accom-panied by the elimination of LiX and the migration of Me. The borate 2b reacts with HCl to give a mixture of the isomers R₂B-B(CH₂SiMe₃)=NHR (4d) and R(Me₃SiCH₂)-B-BR=NHR (4d′), and 2c reacts with HCl to yield the borane R(Me₃CCH₂)B-BR=NHR (4e′) exclusively. The transformation of [R₂R′B-B≡NR]^- to R₂B-BR′ =NRE by the attack of electrophiles E corresponds to the known transformation of [R₃^′B-C≡CR″]^- to R₂^′B-CR′ = CR″E. VCH Verlagsgesellschaft mbH, 1996.