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Schäfer M, Beattie NA, Geetharani K, et al. Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-tert-butyliminoborane and Alkynes. J Am Chem Soc. 2016;138(26):8212-20doi: 10.1021/jacs.6b04128.
Schäfer, M., Beattie, N. A., Geetharani, K., Schäfer, J., Ewing, W. C., Krahfuß, M., Hörl, C., Dewhurst, R. D., Macgregor, S. A., Lambert, C., & Braunschweig, H. (2016). Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-tert-butyliminoborane and Alkynes. Journal of the American Chemical Society, 138(26), 8212-20. https://doi.org/10.1021/jacs.6b04128
Schäfer, Marius, et al. "Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-tert-butyliminoborane and Alkynes." Journal of the American Chemical Society vol. 138,26 (2016): 8212-20. doi: https://doi.org/10.1021/jacs.6b04128
Schäfer M, Beattie NA, Geetharani K, Schäfer J, Ewing WC, Krahfuß M, Hörl C, Dewhurst RD, Macgregor SA, Lambert C, Braunschweig H. Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-tert-butyliminoborane and Alkynes. J Am Chem Soc. 2016 Jul 06;138(26):8212-20. doi: 10.1021/jacs.6b04128. Epub 2016 Jun 27. PMID: 27286231.
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J Am Chem Soc. 2016 Jul 06;138(26):8212-20. doi: 10.1021/jacs.6b04128. Epub 2016 Jun 27.

Synthesis of Functionalized 1,4-Azaborinines by the Cyclization of Di-tert-butyliminoborane and Alkynes.

Journal of the American Chemical Society

Marius Schäfer, Nicholas A Beattie, K Geetharani, Julian Schäfer, William C Ewing, Mirjam Krahfuß, Christian Hörl, Rian D Dewhurst, Stuart A Macgregor, Christoph Lambert, Holger Braunschweig

Affiliations

  1. Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.
  2. Institute of Chemical Sciences, Heriot-Watt University , Edinburgh EH14 4AS, U.K.
  3. Insitute für Organische Chemie, Julius-Maximilians-Universität Würzburg , Am Hubland, 97074 Würzburg, Germany.

PMID: 27286231 DOI: 10.1021/jacs.6b04128

Abstract

Di-tert-butyliminoborane is found to be a very useful synthon for the synthesis of a variety of functionalized 1,4-azaborinines by the Rh-mediated cyclization of iminoboranes with alkynes. The reactions proceed via [2 + 2] cycloaddition of iminoboranes and alkynes in the presence of [RhCl(PiPr3)2]2, which gives a rhodium η(4)-1,2-azaborete complex that yields 1,4-azaborinines upon reaction with acetylene. This reaction is compatible with substrates containing more than one alkynyl unit, cleanly affording compounds containing multiple 1,4-azaborinines. The substitution of terminal alkynes for acetylene also led to 1,4-azaborinines, enabling ring substitution at a predetermined location. We report the first general synthesis of this new methodology, which provides highly regioselective access to valuable 1,4-azaborinines in moderate yields. A mechanistic rationale for this reaction is supported by DFT calculations, which show the observed regioselectivity to arise from steric effects in the B-C bond coupling en route to the rhodium η(4)-1,2-azaborete complex and the selective oxidative cleavage of the B-N bond of the 1,2-azaborete ligand in its subsequent reaction with acetylene.

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