Phosphonium salts alkynes

Phosphonium salts can be synthesized by the transition-metal-catalyzed addition reaction of triaryphosphines and acids to unsaturated compounds. The reaction of PPh3, CH3SO3H, and alkynes in the presence of a palladium or rhodium catalyst gave alkenylphosphonium salts. Although Pd(PPh3)4 directed the C-P bond formation at the internal carbon atom of aliphatic 1-alkynes (Markovnikov mode), [RhCl(cod)]2... 

The same situation is encountered with a,/ -alkynic phosphonium salts in which C(a) carbons are strongly shielded vs C p) carbons 47.8-73.0 vs 119-127 ppm36,97. The linear correlation of the C(a) and C(P) chemical shifts with a para Hammet constant was illustrative of the polarization of the 7r-electron system in the C=C triple bond (Figure 8). In the same sense, the observed C(flt) and C(/J) chemical shifts were used to argue for the existence of either resonance hybrid structures as in the case of enaminophosphonium salts98,99 or incipient ylide contribution40. 

Difluorocarbene can be conveniently generated at room temperamre by the addition of fluoride ion to bromodifluorophosphonium bromide and, provided that the solvents are scrupulously dry, can be trapped by alkenes [60], dienes [61] and cycloalkenes [62] (Figure 6.42). The phosphonium salt may be generated in situ, allowing cyclopropanation to be carried out in a one-pot process [60] (Figure 6.43). Addition of 18-crown-6 to the reaction medium enhances the solubility of the metal fluoride and allows cyclopropanation of less nucleophilic alkenes and alkynes to be performed [63] (Figure 6.44). 

Reactions of Phosphines. - 1.2.1 Nucleophilic Attack at Carbon. Treatment of the unsaturated y-lactone (177) with tributylphosphine results in selective relacement of chlorine to form the phosphonium salt (178). Reactions of phosphines with alkynes have continued to attract interest. A palladium-catalysed addition of triphenylphosphine to unactivated terminal alkynes in the presence of methanesulfonic acid provides a route to the vinylphosphonium salts (179). This reaction fails with methyldiphenylphos-... 

Kawamoto, A.M., and Campbell, M.M., A new method for the synthesis of a phosphonic acid analogue of phosphoserine via a novel 1,1-difluorophosphonate intermediate, J. Fluorine Chem.. 81, 181, 1997. Burton, D.J., Naae. D.G., Flynn, R.M., Smart, B.E., and Brittelli, D.R.. Phosphine- and phosphite-mediated difluorocarbene exchange reactions of (bromodifluoromethyl)phosphonium salts. Evidence for facile dissociation of (difluoromethylene)triphenylphosphorane. J. Org. Chem.. 48. 3616, 1983. Li, A.-R., and Chen. Q.-Y., Diethyl iododifluoromethylphosphonate. A new synthetic method and its reaction with alkynes. Synthesis, 606, 1996. 

Hunig bases, polymeric = animated cbloro-methylated ethenylbenzene homopolymers deprotonation with of ketones, 11 or phosphonium salts, 32 removal of acids with, 32 Hybrid plasmids, 243-245 Hydration. See Alkenes or Alkynes Hydrazine hydrazinolysis with of esters, 239-240,331 of phthaloyl-protected amines, 162,163 reduction of ketones with, 97-98,109 Hydrazines, cyclic oxn., N3 extrusion, 35,331 Hydrazones WolfF-Kishner redn. of, 109 —, aryl- indole synth. with, 151-152, 296, 307 —, dialkyl-, lithiated alkylation, 12, 18, 25-26 enantioselective (SAMP-hydrozones), 25-26 ozonolysis of, 26... 

The Huisgen 1,3-dipolar cycloaddition of azides to alkynes or nitriles as dipolaro-philes, resulting in 1,2,3-triazoles or tetrazoles, is one of the most powerful click reactions . A limitation of this approach, however, is the absence of regiospecificity normally found in thermal 1,3-cycloaddition of nonsymmetrical alkynes this leads to mixtures of the different possible regioisomers. In other reports, classical 1,3-dipolar cycloadditions of azides to metal acetylides, alkynic Grignard reagents, phosphonium salts and acetylenic amides have been described. Extended reaction times and high temperatures are required in most of the reactions, but they can also be performed more effectively with the aid of microwave irradiation. The main results reported are reviewed in this section. 

In a related synthesis of phosphonium salts, Pd2(dba)3 catalyzed addition of alkenes and the acid Tf2NH to PPhs to yield anti-Markovnikov adducts (Scheme 61) [108]. By analogy to related chemistry with alkynes [109], a plausible mechanism involves protonation of Pd, alkene insertion, and P-C reductive elimination. 

SoHd-liguid phase-transfer catalysis. Crown ethers have commonly been used as catalysts for reactions between a solid-liquid interface, and quaternary ammonium and phosphonium salts have been used only as catalysts for reactions in two-phase liquid liquid reactions. However, several laboratories have reported that the latter catalysts are also satisfactory for two-phase solid liquid reactions. Thus dichlorocarbene can be generated from chloroform and solid sodium hydroxide under catalysis from benzyltriethylammonium chloride in yields comparable to those of the classical Makosza method. Another example of this type of catalysis is the oxidation of terminal and internal alkynes by solid potassium permanganate in CH2CI2 with Adogen 464 as catalyst. Aliquat 336 has been found to be as satisfactory as a crown ether for certain displacement reactions with NaOAc, KSCN, KNOa, and KF in CH3CN or CHaCla. ... 

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