Triphenylphosphine reductive coupling

The deoxygenation of epoxides is not of great preparative value since it involves some loss of stereochemical integrity and the alkenes produced are more readily approached in other ways. Reductive cleavage of ozonides, for example, using triphenylphosphine, commonly forms part of the ozonolysis procedure for conversion of alkenes into carbonyl compounds. If a carbonyl compound is treated with an appropriate P(III) reagent then the reverse process may occur—reductive coupling to form a new C=C double bond. This has found a particularly important... 

The use of tris(o-tolyl) phosphite in place of triphenylphosphine has been found to favour the reductive coupling of the metal-coordinated methylallyl (or of the cyanobutyl group in the second step) with the CN group, which liberates the metal in its original (0) oxidation state. 

Reductive coupling of allylic halides. This cobalt complex (1 equiv.) effects reductive coupling of allylic halides to form 1,5-dienes with preservation of the geometry of the double bonds/ The major product from coupling of terpenoid allylic halides is that formed by head-to-head coupling. The triphenylphosphine liberated during the reaction is removed as methyltriphenylphosphonium iodide, obtained by reaction with methyl... 

Nickel(O) triphenylphosphine species have been used to convert allyl halides to 1,5-hexadiene [332], for the reductive coupling of ethylene with aryl halides to give 1,1-diaryl-ethanes [333], and for the coupling of aryl halides and alkenes to prepare substituted olefins [334], In addition, l,2-bis[(di-2-propylphosphino)benzene]nickel(0) has been used for the reductive coupling of aryl halides [335], and l,2-bis[(diphenylphosphino)ethane]-nickel(O) has been employed to synthesize biphenyl from bromobenzene [336] and to prepare benzoic acid from bromobenzene in the presence of carbon dioxide [337]. 

A five-step chemical modification of 51 gives A,0-protected a-amino-a -hydroxy-ketone 54. Difluorination of the ketone 54 at the carbonyl carbon with morpho-DAST followed by conventional chemical modification results in the synthesis of P-amino-a,a-difluorocarboxylic acid 55 (see Scheme 9.13) [31]. Enantiomerically pure 5,5,5,5, 5, 5 -hexafluoroleucine 57 is efficiently synthesized from Garner s aldehyde 52 as shown in Scheme 9.14 [32]. Triphenylphosphine-induced reductive coupling of 52 with hexafluo-rothioacetone produces 56 in an excellent yield, which is conventionally transformed to... 

The C—C bond formation in these complexes is reversible. Treatment of the butadiene or isoprene derivatives with molten triphenylphosphine leads to diene evolution, in moderate yields, but reductive coupling of the M—C bonds occurs when the complexes are reacted with CO at low T since 4-vinylcyclohexene is formed . An unstable olefin complex can be formed from divinylcyclobutane and (cyclododecatriene)Ni(tricyclohexylphosphine) that liberates divinylcyclobutane when... 

Modifications of C6 of CyD other than by tosylation are very rare. However, a single-step quantitative-yield synthesis of CyD monoaldehydes has been published. The CyD was dissolved in an organic solvent, Dess-Martin perodinane was added, and the mixture was stirred for 1 h at room temperature. Addition of acetone and cooling allowed isolation of the crude product by filtration [16]. Another synthesis was performed by using IBX (l-hydroxy-l,2-benziodoxol-3(lH)-one 1-oxide) as oxidant in DMSO. Mono-oxidation of jS-CyD was performed along with its incorporation into chitosan by a reductive coupling reaction [17]. A direct azidation of CyDs with sodium azide in the presence of triphenylphosphine-carbon tetrabromide has also been reported [18]. 

Alkyl(triphenylphosphine)gold(l) complexes are stable and exist in solution as monomeric species (Whitesides et al., 1971, 1974), Reductive coupling of //-alkylgold(I) gives the corresponding dimeric alkanes in high yields. A detailed study with the methylgold complex has demonstrated operation of a... 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

Because the Sonogashira coupling process outlined in Scheme 18 is initiated by the in situ reduction of palladium(n) to palladium(o), it would be expected that palladium(o) catalysts could be utilized directly. Indeed, a catalytic amount of tetrakis(triphenylphosphine)-... 

In the direct coupling reaction (Scheme 30), it is presumed that a coordinatively unsaturated 14-electron palladium(o) complex such as bis(triphenylphosphine)palladium(o) serves as the catalytically active species. An oxidative addition of the organic electrophile, RX, to the palladium catalyst generates a 16-electron palladium(n) complex A, which then participates in a transmetalation with the organotin reagent (see A—>B). After facile trans- cis isomerization (see B— C), a reductive elimination releases the primary organic product D and regenerates the catalytically active palladium ) complex. 

Adamantylideneadamantane has been prepared by (1) photolysis of 2-adamantylketene dimer,2 (2) reduction of 4< -chloroadaman-tylideneadamantane with sodium in liquid ammonia,3 (3) rearrangement of spiro[adamantane-2,4 -homoadamantan-5 -ol] with Lewis acids,4,5 (4) reduction of 2,2-dibromoadamantane with magnesium6 or zinc-copper couple,7 and (5) treatment of the azine of 2-ada-mantanone with hydrogen sulfide, followed by oxidation with lead tetraacetate and heating with triphenylphosphine.8... 

---