Hydroboration of isoprene and 1,4-cyclooctadiene with N-azolylboranes

Article abstract of DOI:10.1016/S0022-328X(96)06920-3

The hydroboration of isoprene with N-azolylboranes in THF [az-BH₂-THF: az = N-pyrrolyl (1a), N-2,5-dimethylpyrrolyl (1b), N-indolyl (1c), N-carbazolyl (1d)] affords the boracyclopentane derivatives 2a-d. In the case of 2b,c, the reduced species 3b,c with a 2,5-dimethylpyrrolidinyl and a 2,3-dihydroindolyl group respectively attached to the boron atom are also present as side products. The hydroboration of 1,4-cyclooctadiene with 1a-c leads to mixtures of products containing both the 9-borabicyclo[3.3.1]nonane (6a-c) and the 9-borabicyclo[4.2.1]nonane derivative (7a-c). In the case of the reaction of 1d with 1,4-cyclooctadiene, the 9-(N-carbazolyl)-9- borabicyclo[4.2.1 ]nonane 7d is formed selectively. The reaction of the corresponding tetraalkyldiboranes(6) with the azoles gives the boracyclopentane derivatives 2 and 4 in higher purity, and in the case of (H-9-BBN)², all 9-(N-azolyl)-9-borabicyclo[3.3.1]nonanes 6a-d are obtained as the sole products.