Convenient method for the preparation of catecholborane and promotion of the formation of alkenyl catecholborane using BH3 complexes

Catecholborane is prepared in benzene by passing B₂H₆, generated from I₂/NaBH₄, through a suspension of catechol at 25°C. The reagent prepared in this way is used for hydroboration-oxidation of representative alkenes and alkynes at 80°C. Hydroboration of 1-alkynes followed by iodination with I₂/NaOH gives the corresponding trans-1-alkenyl iodides in 70–72% yield. The alkenyl catecholboranes can be prepared at 25°C by performing the reaction in the presence of 10 mole% of H₃B:N(C₂H₅)₂Ph or H₃B:THF. The reaction is believed to go through hydroboration of the alkynes by borane followed by exchange with catecholborane. Studies of the preparation of dialkylphenoxyboranes and alkenyldiphenoxyboranes through hydroboration of 1-decene and 1-decyne by use of H₃B:N(C₂H₅)₂Ph and phenol are also reported.