Description:
<jats:title>Abstract</jats:title><jats:p>1‐Alkynyl(diethylamino)dimethylsilanes [CC̊: R = Me (<jats:bold>1a</jats:bold>), <jats:italic>n</jats:italic>Bu (<jats:bold>1b</jats:bold>), SiMe<jats:sub>3</jats:sub> (<jats:bold>1c</jats:bold>)] react with triethylborane stereoselectively by 1,1‐ethyloboration to give the alkenes with the boryl and silyl group in <jats:italic>cis</jats:italic>‐positions at the C=C bond. Owing to the strongly intramolecular coordinative N‐B bond, these products are 2,5‐dihydro‐1,2,5‐azoniasilaboratoles (<jats:bold>2a‐c</jats:bold>). Protic reagents such as azoles (indole, pyrazole, imidazole, triazole, indazole, benzotriazole) react with <jats:bold>2</jats:bold> to give diethylamine and the respective <jats:italic>N</jats:italic>‐azolyl derivatives <jats:bold>3–8</jats:bold> which contain tetracoordinate boron in the case of <jats:bold>4–8</jats:bold>. Compound <jats:bold>7</jats:bold>, derived from indazole, was characterized by an X‐ray analysis. With ethanol, the corresponding 2,5‐dihydro‐1,2,5‐oxoniasilaboratoles <jats:bold>9</jats:bold> are obtained. Treatment of <jats:bold>2</jats:bold> with water affords 1,2,5‐oxasilaborolanes <jats:bold>11</jats:bold>, presumably via an intermediate <jats:bold>10</jats:bold> with the structure of a 2,5‐dihydro‐1,2,5‐oxoniasilaboratole. All products were characterized by their <jats:sup>1</jats:sup>H‐, <jats:sup>11</jats:sup>B‐, <jats:sup>13</jats:sup>C‐, <jats:sup>15</jats:sup>N‐, and <jats:sup>29</jats:sup>Si‐NMR data.</jats:p>