Reduction of CO₂ to Trimethoxyboroxine with BH₃ in THF

Commercially available THF solutions of BH₃·THF, which contain 0.5 mol % of NaBH₄ as a stabilizing reagent for BH₃·THF, react with 1 atm of CO₂ at room temperature to form trimethoxyboroxine, (MeOBO)₃, in 87% yield after 12 h. Since no reaction took place in the absence of NaBH₄, NaBH₄ was found to work as a promoter or catalyst for the reduction of CO₂ with BH₃ to the methoxy compound. A similar reaction using HCOONa in place of NaBH₄ also gave (MeOBO)₃ in comparable yield.