Tris phosphine, conversion

A common way to generate a chiral catalyst involves a modification of Wilkinson s catalyst (340) in which an optically active tertiary phosphine, bis- or tris-phosphines are used as ligands in place of triphenyl-phosphine. If the phosphorous atom of the added phosphine is the stereogenic center, the optical yields are usually 4-22%, as in the conversion of atropic acid (447) to hydratropic acid (448) with 22% ee." " " An example of this type of phosphine is (-)-methylpropylphenylphosphine. bis(Phosphines) are commonly used, including 449 (called dipamp)" " and 450 (called R-camp)." " ... 

A twofold intramolecular Heck reaction of the dibromobenzene derivative 19 has been used to construct the heptacyclic skeleton 20 of cephalostatin analogs. This reaction required a precise control of the reaction time and temperature. The conversion proceeded best with a catalytic amount of the palladacycle from tris(< -tolyl)phosphine and palladium acetate, and gave exclusively (in 80% yield) the heptacycle 20 with an unusual m-annelation of the two newly formed rings (Scheme 10). ... 

A phosphorus atom replaces oxygen when the pyrylium salt is treated with one of several nucleophilic phosphines for example, tris(trimethylsilyl)phosphine gives 2,4,6-triphenylphosphorin (80) (67AG(E)458). The earliest use of 2,4,6-tri-r-butylpyrylium tetrafluoroborate (81) was its conversion to the corresponding phosphabenzene (82) (68AG(E)461). 

The radical reductive cyclisation of diesters to acyloins (see also Section 5.9.1, p. 628) is an important method of synthesis for ring sizes from four-membered upwards. The example selected here is 2-hydroxy-3-methylcyclopent-2-enone ( corylone ) (29) (Expt 7.10), which is an important perfumery and flavouring material.53 In the first step (i), methyl acrylate is converted into its dimer with tris(cyclohexyl)phosphine in pyridine solution.5b Step (ii) is the protection of the double bond by conversion into the dimethylamino adduct. The acyloin reaction is step (iii), and the product is trapped as its bis(trimethylsilyl)ether. Finally, in step (iv), the protecting dimethylamino and trimethylsilyl groups are removed by passage down a column of silica gel. 

Fig. 10 Activity of different phosphine ligands in the palladium-catalyzed telomerization of glycerol. The tris(o-methoxyphenyl)phosphine gives the best results in terms of conversion and activity [32]...

Homoallylic alcohol 1459 was obtained in 64% yield from 5-iodo-l-methylindole 1458 (1.5 mmol), allene (1.0bar) and 4-methoxybenzaldehyde (l.Ommol) (DMF, 80°C, 18h, Schlenk tube) in the presence of indium (100 mesh powder, 1.5 mmol), Pd(OAc)2 (0.1 mmol) and tris(2-furyl)phosphine (0.2 mmol) (Equation 303) <2000CC645>. The use of triphenylphosphine resulted in an incomplete conversion of the starting materials. 

Primary and secoiidary nitroalkanes. A new route to nitro compounds involves conversion of azides to phosphine imines by reaction with triphenyl- or tri-n-butylphos-phine at 25—35° followdd by ozonolysis in CHiCE at — 78°. Presumably the initial ozonidc is converted into a nitfoso compound, which is then oxidized to the nitro compound... 

THIOACETALS Methyl iodide. Silver oxide. Tricthyloxonium tetrafluoroborate. CONJUGATE ADDITION Cuprous bromide. Dimethylcopperlithium. Tri-n-butyl-phosphine-copperfl) iodide complex. CONVERSION OF - Br TO - OIID Silver sulfate. 

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