Summary
The reactions of phosphinylidene-containing compounds with unactivated unsaturated hydrocarbons are reviewed. The review is organized by phosphorus-containing functional group types. Free-radical and metal-catalyzed additions of R1R2P(O)H to alkenes, alkynes, and related compounds, deliver functionalized organophosphorus compounds RP(O)R1R2, including H-phosphinates, phosphinates, tertiary phosphine oxides, and phosphonates. The review covers the literature up to February 2008.
Access to P-chiral H-phosphinates via desymmetrization of hypophosphite esters was investigated. The use of chiral auxiliaries, chiral catalysts, and of a bulky prochiral group that could lead to kinetic resolution was explored. A chiral NMR assay for enantiomeric excess determination of H-phosphinates was developed. An asymmetric route to C-chiral H-phosphinates is also examined and an assay was developed.
A novel catalytic allylation of H-phosphinic acids is described. Using Pd/xantphos (2 mol %), H-phosphinic acids react directly with allylic alcohols to produce P-allylated disubstituted phosphinic acids.
Benzylic alcohols cross-couple directly with concentrated H3PO2 using Pd/xantphos (1 or 2 mol-%). Depending on the substrate, DMF at 110°C, or t-AmOH at reflux with a Dean-Stark trap, can be used. A broad range of benzylic alcohols reacted successfully in moderate to good yields. The preparation of other organophosphorus compounds (phosphinic and phosphonic acids) is also demonstrated.
Asymmetric reaction with (R)-1-(2-naphthyl)ethanol provided the corresponding H-phosphinic acid in 77% ee. The methodology provides a green, PCl3-free, entry into benzylic-H-phosphinic acids.
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