Preparation, NMR characterization, and labeling reactions of tritiated borane-THF complex and high specific radioactivity

Borane-tetrahydrofuran complex is a selective, electrophilic reducing agent. The authors report a simple and facile synthesis of tritiated borane-THF complex at high specific radioactivity. Li-3H, synthesized from carrier-free tritium gas and dispersed in dry tetrahydrofuran, was treated with boron trifluoride etherate to produce borane-THF complex (ca. 3060 GBq/mmol). (The maximum theoretical specific radioactivity of tritium is 1063 GBq/milliatom = 28.76 Ci/milliatom.) This complex was used in an exemplary reduction of 2-napthoic acid to 2-naphthalenemethanol, in high yield. Both the borane-THF complex and the reduction product were characterized by a combination of 1H, 3H, and 11B NMR techniques, as appropriate. The reduction product was found to have >94% of the maximum theoretical specific radioactivity, and all of the tritium at the reduced position. 2 figs