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. 2023 May 10;21(18):3778-3783.
doi: 10.1039/d2ob02186b.

The aromatic Claisen rearrangement of a 1,2-azaborine

Hannah M Robichaud  1 , Jacob S A Ishibashi  1 , Tomoya Ozaki  1 , Walid Lamine  2 , Karinne Miqueu  2 , Shih-Yuan Liu  1   2
Affiliations

The aromatic Claisen rearrangement of a 1,2-azaborine

Hannah M Robichaud et al. Org Biomol Chem. .

Abstract

The first aromatic Claisen rearrangement of a 1,2-azaborine is described along with a quantitative kinetic comparison of the reaction of the azaborine with its direct all-carbon analogue. The azaborine A rearranged in a clean, regioselective fashion and reacted faster than the all-carbon substrate B at all temperatures from 140-180 °C. Activation free energies were extracted from observed first-order rate constants (A: ΔG‡298K = 32.7 kcal mol-1; B: ΔG‡298K = 34.8 kcal mol-1) corresponding to a twenty fold faster rate for A at observed reaction temperatures. DFT calculations show that the rearrangement proceeds via a concerted six-membered transition state and that the electronic structure of the BN and CC rings is mostly responsible for the observed regioselectivity and relative reactivity.

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Conflict of interest statement

Conflicts of interest

The authors declare no competing financial interest.

Figures

Fig. 1
Fig. 1
Eyring plots for A and B. Error bars are the standard deviation from the calculated average of five separate measurements.
Fig. 2
Fig. 2
Calculated relative energy profiles for the aromatic Claisen rearrangement for A (C(3) and C(5)-positions, blue) and B (black) computed at SMD(o-DCB)-PBE0-D3(BJ)/6–31G** level of theory. Main distances in Å. Plot of the HOMO of A and main atomic orbital compositions in percents (%).
Scheme 1
Scheme 1
Synthesis of azaborine A.
Scheme 2
Scheme 2
Claisen rearrangement of A is regioselective for the 3-position.
See this image and copyright information in PMC

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