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Controlling Regiochemistry in the Syntheses of Boraindanes from Diborane(4) Starting Materials
Nicole Arnold1, Holger Braunschweig2, William C Ewing1
1Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, 97074, Würzburg, Germany.
Abstract:
The reaction of tert-butylisonitrile (tBuNC) with 1,2-dihalo-1,2-diduryldiborane leads initially to the formation of the mono-base adduct of the symmetrical diborane(4), which then undergoes an intramolecular cyclization resulting in the formation of a 1-boraindane. This result is in contrast to a previously reported cyclization of a mono-isonitrile adduct of an unsymmetrical 1,1-pinacol-2,2-diaryldiborane(4), which results in the formation of a 1-boraindane. This latter result is herein confirmed by the reaction of 1,1-difluoro-2,2-dimesityldiborane(4) with tBuNC, which yielded the 2-boraindane compound. The mechanism of the former reaction has been computationally elucidated, and the differences between this route and the pathway to 1-boraindanes is discussed. These reactions further the understanding of the chemistry of the increasingly popular mono-base adducts of diborane(4), demonstrate the versatility of isonitriles in comparison to standard two-electron donors, and elucidate selective routes to boron-containing polycyclics, such as those being proposed as analogues for conventional organic pharmaceuticals.
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