871-95-4Relevant articles and documents
Improved Synthetic Route to Heteroleptic Alkylphosphine Oxides
Kendall, Alexander J.,Seidenkranz, Daniel T.,Tyler, David R.
supporting information, p. 2412 - 2417 (2017/07/17)
A new method for the synthesis of heteroleptic alkylphosphine oxides (R2R1P=O, where R ≥ R1) from secondary phosphine oxides (or SPOs, R2HP=O) is presented. These reactions were fast at room temperature, sterically selective, high yielding, and >95% pure after an aqueous wash. Deprotonation of an SPO generates a phosphinite anion ([R2P-O]-) that was found to be highly selective for nucleophilic P-C bond formation (as opposed to O-C bond formation) with alkyl halides. Surprisingly, most strong organometallic bases failed to deprotonate SPOs to their respective phosphinite anions (pKas for most SPOs are a very specific base to deprotonate suggests that both ion pairing and the conjugate acid play a role in stabilizing the phosphinite anion. Phosphinite anion reactivity followed the expected trend for an SN2 mechanism on reaction with alkyl halides; elimination products were never observed. A wide variety of heteroleptic alkylphosphine oxides were isolated in near-quantitative yield with only an aqueous wash as purification. This methodology was then used to make new bis(phosphine oxide)alkanes and unsymmetrical α,ω-bis(phosphine oxide)alkanes (R2P(O)(CH2)3P(O)R12) on the benchtop with unprecedented ease.
