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33.5.4.1.1.2 Variation 2: Radical-Catalyzed Hydrophosphination

DOI: 10.1055/sos-SD-033-00794

Gaumont, A. C.; Gulea, M.Science of Synthesis, (200733713.

The free-radical addition of phosphines to alkynes was described as early as 1952. The reaction generally occurs in an anti-Markovnikov fashion, giving the β-adduct.[‌28‌] For example, diphenylphosphine reacts with various terminal alkynes (phenylacetylene, pent-1-yne, or 3,3-dimethylbut-1-yne) and one internal alkyne (1-phenylpropyne)[‌29‌] in the presence of a catalytic amount of 2,2-azobisisobutyronitrile or upon UV irradiation to give the corresponding alk-1-enylphosphines in modest to good yields (1573%) (Scheme 4). The primary products formed are the E-anti-Markovnikov adducts (E)-3 (the kinetic products), but the main isolated products are the Z-anti-Markovnikov adducts (Z)-3 (the thermodynamic products);[‌29‌] the Markovnikov products 4 are also often formed. Water-soluble phosphines can be similarly prepared in modest yields by addition of diphenylphosphine to alkynols or alkynyl ethers.[‌29‌,‌30‌] When the heteroatom is directly bonded to the α-atom, the reaction is highly regioselective. With other derivatives a mixture of regioisomers is obtained.[‌29‌] With 1,5-diynes and primary phosphines, 4,5-dihydrophosphepines are formed.[‌31‌]

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