Reduction of CO<sub>2</sub> to Trimethoxyboroxine with BH<sub>3</sub> in THF

Commercially available THF solutions of BH<sub>3</sub>·THF, which contain 0.5 mol % of NaBH<sub>4</sub> as a stabilizing reagent for BH<sub>3</sub>·THF, react with 1 atm of CO<sub>2</sub> at room temperature to form trimethoxyboroxine, (MeOBO)<sub>3</sub>, in 87% yield after 12 h. Since no reaction took place in the absence of NaBH<sub>4</sub>, NaBH<sub>4</sub> was found to work as a promoter or catalyst for the reduction of CO<sub>2</sub> with BH<sub>3</sub> to the methoxy compound. A similar reaction using HCOONa in place of NaBH<sub>4</sub> also gave (MeOBO)<sub>3</sub> in comparable yield.