Nucleophilic and free-radical additions of phosphines and phosphine chalcogenides to alkenes and alkynes

Nucleophilic and free-radical additions of phosphines and phosphine chalcogenides to alkenes and alkynes are discussed. The bibliography includes 169 references.


Introduction
6][17][18] Over the recent years, a lot of research has been devoted to addition reactions of P-H reagents to multiple carbon-carbon bonds, catalyzed by metal complexes, and, as a result, numerous synthetic methods have been developed (for example, see the reviews [19][20][21][22][23] ).Meanwhile, hydrophosphination of alkenes and alkynes under base-catalyzed or free-radical conditions (i.e., under "green chemistry" conditions) often appears to be competitive, let alone ecologically safer, and sometimes experimentally even more advantageous.
In this review, we survey and analyze results of the investigations concerning the heavy metal-free additions of phosphines and phosphine chalcogenides, containing a P-H function, to multiple carbon-carbon bonds.The attention is focused on the work of the last 10 years, relating to synthesis of functional phosphines and phosphine chalcogenides through reactions of phosphine, primary and secondary phosphines, phosphine oxides and sulfides with substituted alkenes and alkynes.For this period a number of new or earlier inaccessible P-H species became readily available owing to the methodology for the activation of elemental phosphorus in heterogeneous strongly basic media 24,25 developed in late 80-s [26][27][28][29][30][31] (now often referred to as the Trofimov-Gusarova reaction 32,33 ).5][36][37][38] Some of the P-H compounds derived from these reactions turned out to be rewarding addends for nucleophilic and free-radical additions to multiple bonds, thus further unfolding the field.

ARKAT
examples of nucleophilic addition to such electron-rich double bonds.Unfortunately, the paper 86 does not contain any data proving the structures of the compounds obtained.
The system KOH-DMSO also allowed the reaction of 3-thiolene-1,1-dioxide (14a) with primary phosphines 96 and secondary phosphine chalcogenides 5a, 15 97,98 to be carry out.The corresponding adducts were synthesized in high yield.Without KOH or under radical conditions [65 o C, 6 h, azabisisobutyronitrile (AIBN)], neither hydrophosphination nor hydrophosphorylation occurs, thus confirming the nucleophilic character of this addition, which, presumably, proceeds via the formation of intermediate 2-thiolene-1,1-dioxide (14b) (Scheme 7). 97,98  15 2.2 Radical addition of phosphines and phosphine chalcogenides to alkenes 2.2.1 Phosphine.Addition of phosphine to alkenes under radical conditions (organic peroxides, AIBN, UV irradiation) was published mainly as patents and discussed in a review. 4epresentative recent investigations are the synthesis of limonene-derived chiral phosphines 99 and polyfunctional tertiary phosphines and phosphine oxides from vinylsulfides. 100 The use of phosphine-hydrogen mixture 53 generated in situ from elemental phosphorus in the latter case demonstrates applicability of this available phosphorylating reagent also for free-radical addition reactions. 100hus, the phosphine-hydrogen mixture generated from red phosphorus in the system KOHtoluene-H 2 O, reacts readily with vinyl sulfides under free-radical conditions (dioxane, AIBN, 65-70 o C, atmospheric pressure) to give regiospecifically anti-Markovnikov adducts, tris [2-(organylthio)ethyl]phosphines (16) (Scheme 8). 100 The latter easily oxidize by air during their isolation and purification on Al 2.2.2Primary and secondary phosphines.Addition of primary and secondary phosphines to alkenes (linear unsubstituted alkenes 101 with terminal double bonds and, less often, internal ones, as well as cycloalkenes, 101 aryl-and hetarylalkenes, 101,102 dienes, 101 vinyl 40,41,101 and divinyl 103 ethers, vinylsulfides, 104,105 vinyl phosphines, 106,107 unsaturated organohalides, 108 acrylic acid derivatives 101, 109 etc) under free-radical conditions is widely used in organophosphorus synthesis. 110This pathway allows one to obtain phosphines with hydrophilic substituents, 62,101,102,109,111,112 including water-soluble phosphines, di-and polyphosphines, 106,107,113  Hydrophosphination of vinyl ethers, 41 vinyl sulfides 105 and vinyl selenides 105 with secondary phosphines 1a,g, 18, prepared from elemental phosphorus and electrophiles in superbase systems, 53,117  With air or elemental sulfur the phosphines 20a,b quantitatively oxidize to the corresponding phosphine oxides or phosphine sulfides, respectively. 118Polydentate phosphines, phosphine oxides and phosphine sulfides thus obtained, containing protected hydroxy functionalized tetrahydrofuran and dioxolane moieties, are promising chelating ligands for metal complex catalysts for asymmetric synthesis.
Recently, first examples of the hydrophosphinations of available 24, 25 N-vinyl-and Nisopropenylpyrroles have been reported. 119,120 123] UV 22

Scheme 13
The chemo-and regioselective addition of secondary phosphine sulfides to alkyl vinyl ethers contributes to better understanding the reactivity of the both classes of compounds and offers a facile straightforward route to potent cocatalysts and "hemilabile" ligands 137 (e.g., triphenylphosphine sulfide is more effective ligand for palladium-catalyzed bisalkoxycarbonylation of olefins than triphenylphosphine 138 ).
Later, free-radical addition of diphenylphosphine sulfide to butyl vinyl ether was realized using Et 3 B/O 2 as the initiator. 135Apart from alkenes with electron-rich double bonds, the authors also used a set of alkenes with electron-poor double bonds to prepare phosphine sulfides 26 (Scheme 14).

Nucleophilic addition of phosphines and phosphine chalcogenides to alkynes
Addition of P-H reagents to acetylenes 4,47,93,101,109, is a convenient and atom-economic method of the C-P bond formation and the simplest route to unsaturated phosphines. At the ame time, this field still remains poorly explored and existing publications are mostly related to nucleophilic addition of phosphines and phosphine chalcogenides.4, 47, 93, 139-142, 144, 146-149, 151-153, 155-163

Phosphine
The data on the addition of phosphine to the triple carbon-carbon bond are limited to reports concerning phosphorylation of aryl-and hetarylalkynes in the presence of superbase. 4,153,155 Te reaction proceeds under mild conditions (55-60°C, atmospheric pressure) upon passing phosphine-hydrogen mixture generated from red phosphorus and potassium hydroxide in aqueous dioxane through the reaction mixture to give stereoselectively tris(Z-2organylethenyl)phosphines ( 27) in 60-80% yields (Scheme 15). 153,155 he stereodirection of these reactions agrees with the common trans-addition scheme. 25,34

Scheme 17
Activated phenylcyanoacetylene reacts with alkylphosphines under milder conditions (KOH-dioxane suspension, 20-22 o C) to afford, depending on the reactant ratio, either secondary 29 or tertiary 30 phosphines of Z-configuration in the yield of 70-91% (Scheme 18). 160ccording to ESR and UV data, the addition involves a single electron transfer. 160

Scheme 21
Only E-isomers of ethenylphosphines Alk 2 PCH=CHCO 2 Me are formed in the reaction of dialkylphosphines with methyl 2-propynoate. 147Authors explain this fact by easy isomerization of the intermediate carbanion.
Non-catalyzed interaction of diphenylphosphine (10a) with dimethyl 2-butynedioate reveals the effect of second strong electron-withdrawing group, which activates double bond of the intermediate monoadduct.As a result, the reaction affords the saturated α,β-diadduct 34

Scheme 22
These reactions of phosphines with activated acetylenes (Schemes 19-22) represent a new general atom-economic approach to the synthesis of versatile reactive building blocks for organic synthesis and prospective polydentate and amphiphilic ligands for design of metal complex catalysts. 77,164 th weakly electrophilic acetylenes, addition of secondary phosphines requires strong bases or high temperature to proceed.
Prolonged heating (100°C, 4 days) of diphenylphosphine and diphenylacetylene afforded E-isomer of the corresponding monoadduct Ph 2 PC(Ph)=CHPh. 141It seems that the formation of E-isomers in this addition 141 as well as in the reaction presented in Scheme 19 151 is thermodynamically controlled, i.e., under the reaction conditions Z-adduct isomerizes to the Eform.

ARKAT
Diphenylphosphine with diphenyl(ethynyl)phosphine Ph 2 PC≡CH in the presence of PhLi furnishes E-Ph 2 PCH=CHPPh 2 in a 72% yield. 47The E-isomer is likely to be formed owing to sterical factors.
Diphenylphosphine (10a) adds to arylacetylenes in the presence of strong bases giving arylethenylphosphines 35 of unknown configuration (Scheme 23). 93,148 rom the 3 J HP coupling, 148 one may assume 165 that the compound 35c is a Z-isomer.

Secondary phosphine chalcogenides
Addition of secondary phosphine chalcogenides to acetylenes 89,93,152,161,163 proceeding in the presence of base catalysts usually results in double addition products.Presumably, this occurs due to the strong electron-withdrawing character of phosphoryl or thiophosphoryl group, which activates double bond of monoadducts toward addition of the second phosphine chalcogenide molecule.

Conclusions
In conclusion, nucleophilic and free-radical additions of now readily available phosphines and their chalcogenides to alkenes and alkynes are attracting increasing attention as heavy-metal free and atom-economic syntheses of valuable, and otherwise inaccessible, functionalized phosphines and phosphine chalcogenides.