Rapid Metal‐Free Formation of Free Phosphines from Phosphine Oxides

Abstract

A rapid method for the reduction of secondary phosphine oxides under mild conditions has been developed, allowing simple isolation of the corresponding free phosphines. The methodology involves the use of pinacol borane (HBpin) to effect the reduction while circumventing the formation of a phosphine borane adduct, as is usually the case with various other commonly used borane reducing agents such as borane tetrahydrofuran complex (BH3•THF) and borane dimethyl sulfide complex (BH3•SMe2). In addition, this methodology requires only a small excess of reducing agent and therefore compares favourably not just with other borane reductants that do not require a metal cocatalyst, but also with silane and aluminium based reagents.

Asymmetric Friedel–Crafts Alkylation of Indoles Catalyzed by Chiral Aziridine-Phosphines

“…The corresponding phosphine oxides were synthesized according to protocols reported by us previously [33,34]. It should be also mentioned that attempts at reduction of phosphine oxides using other reducing agents, e.g., Hantzsch ester [39], DIBAL-H [40], pinacol borane (HBpin) [41] or BH3 [42], turned out to be ineffective in our hands.…”

Electroreduction: A Sustainable and Less Energy‐Intensive Approach Compared to Chemical Reduction for Phosphine Oxide Recycling to Phosphine

“…[15] The most common strategies of obtaining TPP from recycling of TPPO are by using chemical reductants like silyl hydrides, [16] aluminium hydrides, [17] boranes, [18,19] and so on. [15,[20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] The bond dissociation energy of the PÀ Cl bond (H 2 PÀ Cl, 315.1 kJ/mol) is less than that of the PÀ O bond (H 2 PÀ OH, 359.7 kJ/mol). Therefore, chlorination of TPPO by oxalyl chloride and/or phosgene followed by reduction by hydrogenation at high pressure in presence of metal catalysts (Pt, Rh, Pd, Na, Fe, Al) remained an alternative approach.…”

Convergent Synthesis of Polysubstituted Furans via Catalytic Phosphine Mediated Multicomponent Reactions

“…First, phosphine oxides are not generally easy to be reduced into the corresponding phosphines at a substantially fast rate under mild conditions; second, the employed reducing agent should be safe for other functional groups of the substrates [29,30]. Consequently, although many new methods for reduction of phosphine oxides have emerged by using reducing agents such as DIBAL-H [31,32], LiAlH 4 [33,34], boron compounds [35][36][37][38], and others [39][40][41][42][43][44][45], applicable ones for catalytic Wittig reactions remain rare. Recently, silanes have been recognized as powerful reducing agents for in-situ deoxygenation of phosphine oxides with good functional tolerance after a series of successful applications of silanes in the transformation of a stoichiometric phosphine-mediated reaction into a catalytic one [46][47][48][49][50][51][52].…”