Recent Developments in Azaborinine Chemistry

Abstract

Recent years have witnessed rapid advances in the field of BN/CC isosterism, particularly in the case of azaborinines. Examples of each isomer have now been synthesized and characterized. This review provides a survey of the latest

Control of Excited‐State Conformations in B,N‐Acenes

“…Similar considerations can be made for one of the smallest possible nitrogen‐containing compounds with such a property, aminoborane (H 2 N−BH 2 ; Figure ). The B−N scaffold has been discussed as C=C surrogate because of its isoelectronic character . However, it has been shown early on that the B−N rotational barrier (29.3 kcal mol −1 ) of aminoborane is much smaller than that of the C=C bond in ethylene (62.5 kcal mol −1 ) .…”

“…In the excited state, the conformation resulting from a 90° rotation around the B−N bond is not the lowest in energy, though. Further relaxation by pyramidalization is more favored owing to negative hyperconjugation resulting in a twisted out‐of‐plane arrangement of the amine . Based on this, we designed a system that would allow favoring an electronic transition to one specific conformer in the excited state (Figure ).…”

Control of Excited‐State Conformations in B,N‐Acenes

“…TheB ÀNs caffold has been discussed as C=Cs urrogate because of its isoelectronic character. [9][10][11][12][13][14] However,i th as been shown early on that the B À Nr otational barrier (29.3 kcal mol À1 ) [2,15] of aminoborane is much smaller than that of the C = Cb ond in ethylene (62.5 kcal mol À1 ). [3,15] Interestingly,a nalogous behavior has been observed for aminoborane theoretically [4,16] as well as experimentally.…”

“…[5][6][7][8]15] In the excited state,t he conformation resulting from a908 8 rotation around the B À Nbond is not the lowest in energy,though. Further relaxation by pyramidalization is more favored owing to negative hyperconjugation [2,[9][10][11][12][13][14]17] resulting in at wisted out-of-plane arrangement of the amine. [3,18] Based on this,w ed esigned as ystem that would allow favoring an electronic transition to one specific conformer in the excited state ( Figure 1).…”

Ring Expansion, Photoisomerization, and Retrocyclization of 1,4,2‐Diazaboroles

“…Thus,i nitial reduction of 2 may generate 4 in situ along with BBr 3 ,which can be reduced by either KC 8 or 4 to yield bromoborylene (BrBD). Tr eatment of 2 with silver triflate (3 equiv) afforded the boronium ion 5 with BBr(OTf) 3 À in 63 %y ield, as decisively confirmed by X-ray diffraction analysis (see Figure S37 b). [19] To confirm the hypothesis,wedecided to isolate 4 by modification of the counterion of 2 (Scheme 1b).…”