3,4-DIMETHYLENEBOROLANES AND 3,7-DIBORABI CYCLO[3.3.0]OCT-1(5)-ENES

The tetramethyleneethane derivative K2[C2(CH2)4] which is readily prep ared from 2,3-dimethylbutadiene by metallation with the Lochmann-Schlo sser base reacts with BCl2(NR2) (R = Me, Et, iPr) to give the highly r eactive, liquid 1-(dialkyl-amino)-3,4-dimethyleneborolanes (3). These dienes react with activated magnesium to give soluble magnesium adduct s 5 which upon treatment with BC12(NR2) (R = Me, iPr) yield crystallin e alkylamino)-3,7-diborabicyclo[3.3.0.]oct-1(5)-enes (4). The crystal structure of the dimethylamino compound 4a was determined by X-Ray-dif fraction. The molecule of 4a shows crystallographic C2h symmetry with an almost perfectly planar skeleton.