Reduction of tertiary phosphine oxides to phosphine-boranes using Ti(Oi-Pr)4/BH3-THF

A new method for reduction of tertiary phosphine oxides leading to the formation of tertiary phosphine-boranes has been developed. The BH3-THF/Ti(Oi-Pr)(4) reducing system enables conversion of triaryl, diarylalkyl and trialkylphosphine oxides directly to their borane analogues in good to high yields. In contrast to the previously reported protocols, the presence of activating groups in the structure of starting material is not necessary for the reaction to occur. The reaction is highly stereoselective and proceeds with predominant retention of configuration at the phosphorus atom. A plausible mechanism of reduction of the P=O bond by BH3-THF/Ti(Oi-Pr)(4) has been proposed. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

A new method for reduction of tertiary phosphine oxides leading to the formation of tertiary phosphine-boranes has been developed, with good to high yields. The reaction is highly stereoselective and retains configuration at the phosphorus atom without the need for activating groups in the starting material structure. A plausible mechanism of reduction of the P=O bond by BH3-THF/Ti(Oi-Pr)(4) has been proposed.