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

Reaction between Cl2AlCH2CH2AlCl2 and BCl3 leads to Cl2BCH2CH2BCl2, in which halogen exchange is achieved by Bl3 to yield I2BCH2CH2BI2 (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 AlMe3 leads to the title compound 1 d , established by 1H, 11B, 13C 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.