Borabicyclo[3.2.0]heptadiene: A Fused Bicyclic Isomer of Borepin

• Published in: Chemistry : a European journal 2018-10, Vol.24 (57), p.15387-15391
• Main Authors: Kelch, Hauke, Kachel, Stephanie, Wahler, Johannes, Celik, Mehmet Ali, Stoy, Andreas, Krummenacher, Ivo, Kramer, Thomas, Radacki, Krzysztof, Braunschweig, Holger
• Format: Article
• Language: English
• Subjects: boranes; cycloaddition; density functional calculations; heterocycles; reaction mechanisms
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.201803509

A new isomer of borepin, identified as 2‐borabicyclo[3.2.0]hepta‐3,6‐diene by single‐crystal X‐ray diffraction and heteronuclear NMR spectroscopy, was obtained by reaction of 1‐mesityl‐2,3,4,5‐tetraphenylborole with the diaminoalkyne bis(piperidyl)acetylene. Analogous reactions of the alkyne with other borole derivatives generated seven‐membered borepins, in which a second equivalent of the alkyne was found to insert into the exocyclic B−C bond. Results of mechanistic DFT studies as well as differences in the reactivity of the boroles toward the diaminoalkyne are discussed. Short Fused: A new isomer of borepin, 2‐borabicyclo[3.2.0]heptadiene, was synthesized by the reaction of a perarylated borole with one equivalent of bis(piperidyl)acetylene (see scheme). Analogous reactions of the alkyne with 1‐phenyl‐ and 1‐thienyl‐2,3,4,5‐tetraphenylborole yielded seven‐membered borepin derivatives, in which the exocyclic B−aryl bond underwent a 1,2‐carboboration with a second equivalent of the alkyne.