Darstellung von 1,2,3,4-Tetramethyl-1,4-diboracyclohexen-2 und Umlagerung zum 1,2,3,4,5-Pentamethyl-2,3-dihydro-1,3-diborol / Synthesis of 1,2,3,4-Tetramethyl-1,4-diboracyclohexene-2 and Rearrangement to 1,2,3,4,5-Pentamethyl-2,3-dihydro-1,3-diborole

Abstract

<jats:p>Reaction between Cl<jats:sub>2</jats:sub>AlCH<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>AlCl<jats:sub>2</jats:sub> and BCl<jats:sub>3</jats:sub> leads to Cl<jats:sub>2</jats:sub>BCH<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>BCl<jats:sub>2,</jats:sub> in which halogen exchange is achieved by Bl<jats:sub>3</jats:sub> to yield I<jats:sub>2</jats:sub>BCH<jats:sub>2</jats:sub>CH<jats:sub>2</jats:sub>BI<jats:sub>2</jats:sub> (5). Redox reaction between butyne-2 and 5 results in the formation of 1,4-diiodo-2,3-dimethyl-1,4-diboracyclohexene-2 (1a) and iodine. Methylation of 1 a with AlMe<jats:sub>3</jats:sub> leads to the title compound 1 d , established by <jats:sup>1</jats:sup>H, <jats:sup>11</jats:sup>B, <jats:sup>13</jats:sup>C NMR. Heating of 1 d in toluene at 160 °C in a sealed tube results in an intramolecular isomerization to give 1,2,3,4,5-pentamethyl-2,3-dihydro-1,3-diborole (2d) in 90% yield.</jats:p>

One‐Pot Synthesis of 1,6‐Diiodo‐2,3,4,5‐tetracarba‐nido‐hexaboranes(6) and Mechanistic Studies on the Reaction System Alkynes/BI3/NaK2.8

“…The redox reaction of 3 with 3‐hexyne shown in Scheme 7 (analogous to the preparation of the corresponding 1,3‐diiodo‐2,3‐dihydro‐1,3‐diborol derivatives23 and the 1,4‐diiodo‐1,4‐diboracyclohexene compounds24) indeed afforded the expected carborane 2a . The reaction mixture showed a broad 11 B NMR signal at δ = 66 ppm.…”