Triphenylphosphine, promoter

The regioselectivity of hydroesterification of alkyl acrylates or aromatic olefins catalyzed by [PdCl2L2] complexes (L = phosphine ligand) could be largely controlled by variation of the ligands. Triphenylphosphine promotes preferential carboxylation to the branched isomer, whereas with bidentate bisphosphines the linear product is produced overwhelmingly [14]. 

Rate data for the triphenylphosphine-promoted dehalogenation of meso-l, -dibromo-l,2-diarylethanes to form ranj-stilbene in DMF are consistent with a concerted unti-elimination mechanism involving the attack of phosphine on bromine. Attack of triphenylphosphine on halogen also occurs in its reaction with the A chIoropyrroiidine-2,5-diones (82), leading eventually to the betaines (83). The... 

The ribofuranosylation of alcohols has been achieved using a base/triphenylphosphine promoted addition of ribofuranosyl iodide to alkyl iodides (Scheme 2.12) [17]. The chemistry was carried out under mild conditions (0 °C) and was highly alpha-selective. Triphenylphosphine was a critical component of the chemistry, and although the precise role of this additive was not fully elucidated, its presence nearly completely suppressed the formation of products resulting from beta-addition. A range of alcohols were successfully functionalized using this approach with excellent selectivity. 

Amatore et al. developed an aqueous cross-coupling reaction of terminal alkynes with 1-iodoalkynes using a water-soluble Pd(0) catalyst prepared in situ from Pd(OAc)2 and sulfonated triphenylphosphine P(C6H4 — m-SCENa (TPPTS) without Cu(I) promoter, giving diynes with moderate yields (43-65%)(Eq. 4.22) 42... 

One of the earliest syntheses of lavendamycin methyl ester, however, did not employ either the Pictet-Spengler or the Bischler-Napieralski reactions for construction of the /J-carboline ring system. Instead, a palladium-promoted ring closure of aryl pyridine 36 (Fig. 12) was used to prepare /1-carboline 37 by Boger and coworkers [35]. Unfortunately, stoichiometric palladium was found to be necessary, in this case 1.5 equivalents of the tetrakis(triphenylphosphine)palladium(0) being used. Friedlander condensation with aldehyde 38 in the presence of benzyltrimethylammonium hydrox-... 

Hydrogenation conditions were optimized by addition of triphenylphosphine as promoter ligand, and the hydrogenation degree of SBS was up to 89%. Hy-... 

The glycosylation based on the Mitsunobu reaction has been most commonly directed to the synthesis of O-aryl glycosides, a structural motif found in a variety of natural products [80-82], Early work by Grynkiewicz [83,84], among others [85-87], established the viability of triphenylphosphine and diethylazodicarboxylate to promote the glycosylation of phenol acceptors at ambient temperature. More recently, Roush and coworkers have discovered that the glycosylation performed well in the... 

Although aliphatic alcohols are typically poor acceptors in the Mitsunobu-type glycosylation, Szarek and coworkers have highlighted one advance to this end [95]. For the triphenylphosphine and diethylazodicarboxylate promoted glycosylation of a monosaccharide acceptor, the addition of mercuric bromide is necessary to promote the reaction. For example, the (1,6)-disaccharide 44 was obtained in 80% yield using this modified Mitsunobu protocol. Unlike previous examples with phenol or N-acceptors, preactivation of the hemiacetal donor was performed for 10 min at room temperature prior to addition of the aliphatic alcohol nucleophile. 

Thus, an achiral promoter for the Cr(0)-mediated [6-1-2] cycloaddition was recently disclosed by Rigby. Here, Cr(0) is attached to the polymeric backbone via immobilized triphenylphosphine [111]. 

As the data summarized in Table 7 indicate, less polar toluene is prone to promote transformation among the species 5 6 7 8, 9, i.e., from a species of a higher coordination number of triphenylphosphine to a lower number. In acetone on the other hand, the quantity of species 5-7 is more sustained even at higher ratios of 4a to Rh (i.e., more similar to the catalytic reaction). 

Similarly the cation (18a), which does not react with alkoxides [75JCS(P1)1260], is protodebrominated by triphenylphosphine, albeit a higher boiling solvent, pentan-l-ol, is required to promote the reaction. The salt (18c), which cannot form a dihydrodiazepine base, also undergoes protodebromination when heated with triphenylphosphine in pentan-l-ol [81AG193, 81AG(E)190]. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

The activity of homogeneous catalysts also has been demonstrated Wilkm son s catalyst tris(triphenylphosphine) rhodium chloride induces petfluoroalkyl iodides to add to olefins at 80 °C [10] (equation 10) Tetrakis(tnphenylphosphme)-palladtum promotes the addition to both alkenes and alkynes in hexane [11] Amines and amine salts induce addition at 120-140 °C [12] (equation 11)... 

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