Synthesis of the first metal-free phosphanylphosphonate and its use in the “phospha–Wittig–Horner” reaction

Abstract

The synthesis of the first phophanylphosphonate, Mes*PH–PO(OEt)₂ (2-H), in which the P(III) centre is not coordinated by a M(CO)₅ (M = W, Mo, Cr) fragment is reported. The title compound reacts with LDA under the formation of 2-Li which is best described as the enolate form with a high double bond character between the two phosphorus centres. 2-Li is shown to engage in the phospha–Wittig–Horner reaction and converts aldehydes into phosphaalkenes that are metal-free and thus available for future manipulations at the phophorus lone pair. Using a selection of aldehydes with aliphatic, aromatic or vinylic substituents as substrates, phosphaalkene formation proceeds in high yields and high E-selectivity. The selectivity is however compromised during purification on standard silica which was found to promote E/Z isomerization.