Reactions phosphine-catalyzed

Morita K, Suzuki Z, Hirose H (1968) A tertiary phosphine-catalyzed reaction of acrylic compounds with aldehydes. Bull Chem Soc Jpn 41(11) 2815-2815... 

Contrary to the phosphine-catalyzed reaction of the allene buta-2,3-dienoate, which adds to CgQ in a ]3-i-2] cycloaddihon ]354], the allene amide 317 forms the cyclobutane annulated fuUerene derivahve in good yields (Scheme 4.63) [355]. The reaction was also performed with similar allene amides bearing a six- or seven-membered lactam. 

Phosphine-Catalyzed Reactions. This ligand has also been shown to be effective in the direct organocatalysis of asymmetric processes. For example, the phosphine-catalyzed [3 -1- 2] annula-tion reaction of ethyl 2,3-butadienoate and isobutyl acrylate produces two cyclopentene regioisomers (1 and 2) (eq 2). Isomer 1 generally predominates and enantiomeric excesses ranging from... 

In contrast to the reported modes of reactions of dienes and allene with tropone, phosphine-catalyzed reaction of modified allylic compounds, including acetates, bromides, chlorides or /er/-butyl carbonates derived from the MBH reaction with tropone, afforded [3 + 6] annulation products 488 in... 

This strategy yielded a small collection ofindoloquinolizines with yields ranging from 20 to 91%. Low yields were observed in the case of halogen-substituted chromones, and the low-yielding step was found to be the phosphine-catalyzed [4-1-2] annulation of 3-formylchromones 36 with acetylene dicarboxylates 37. Therefore, an alternative domino reaction was developed to bypass this phosphine-catalyzed reaction in order to increase the yield of these halogenated indoloquinolizines. 

In situ catalysts formed from Pd(dba)2 precursor and PHOX-type ligands have shown high enantioselectivities in Heck reactions (280). It has to be noted that no C=C double bond migration, a common sidereaction in Pd-phosphine catalyzed reactions, has taken place. 

Scheme 15.47 Au-phosphine-catalyzed reaction of allenamide and primary aryla...

Phosphine-Catalyzed Reactions Enantioselective [3+2] cycloaddition of allenes with enones leads to the synthesis of cyclopentenes, which can be further transformed to cyclopentanes (Scheme 6.4). The phosphine addition to allenoate generates an allylic carbanion, which undergoes addition to the enone in the a and the p positions followed by the phosphine elimination to afford 3 and 4, respeetively [6]. 

Phosphine-Catalyzed Reactions Phosphine-catalyzed [3+2] dipolar cycloaddition has been applied in an intramolecular manner, whereby three contiguous stereogenic centers, including a quaternary center, are created in a single operation (Scheme 6.27). It may be noted that the intramolecular cycloaddition is stereospecific. When the E-isomer is used as the starting material, the quaternary center formed possesses the stereochemistry consistent with the structural features of hirsutene [31]. 

The introduction of the activated allylic bromides and Morita-Baylis-HiUman acetates and carbonates pioneered the development of a number of phosphine-catalyzed reactions in subsequent years [45]. Interestingly, the asymmetric variant of this type of transformation only appeared in the literature seven years later. In 2010, Tang, Zhou, and coworkers disclosed a highly enantioselective intramolecular ylide [3-1-2] annulation using spirobiindane-based phosphine catalyst 31 (Scheme 20.27). BINAP was found inactive in this reaction even at an elevated temperature (70°C). Notably, both optically active benzobicyclo[4.3.0] compounds 32 and 32 with three continuous stereogenic centers could be obtained as major products in high yields and stereoselectivities just by a choice of an additive [Ti(OPr )4], which can block the isomerization of the double bond [46]. 

Although Pd is cheaper than Rh and Pt, it is still expensive. In Pd(0)- or Pd(ll)-catalyzed reactions, particularly in commercial processes, repeated use of Pd catalysts is required. When the products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example. For less volatile products, there are several approaches to the economical uses of Pd catalysts. As one method, an alkyldi-phenylphosphine 9, in which the alkyl group is a polyethylene chain, is prepared as shown. The Pd complex of this phosphine has low solubility in some organic solvents such as toluene at room temperature, and is soluble at higher temperature[28]. Pd(0)-catalyzed reactions such as an allylation reaction of nucleophiles using this complex as a catalyst proceed smoothly at higher temperatures. After the reaction, the Pd complex precipitates and is recovered when the reaction mixture is cooled. 

The palladium-catalyzed reaction of o-iodoanilides with terminal acetylenic carbinols provides a facile route to the synthesis of quinolines using readily available starting materials (93TL1625). When o-iodoanilide 126 was stirred with acetylenic carbinol 127 in the presence of bis-triphenyl phosphine palladium(ll) chloride in triethylamine at room temperature for 24 h, the substituted alkynol 128 was obtained in 65% yield. On cyclization of 128 with sodium ethoxide in ethanol, 2-substituted quinoline 129 was obtained in excellent yield. 

Soderberg and coworkers have developed a palladium-phosphine-catalyzed reductive iV-het-eroannuladon of 2-nitrostyrenes forming indoles in good yields For example, reaction of 6-bromo-2-nitrostyrene with carbon monoxide in the presence of a catalytic amount of palladium diacetate (6 mol% and triphenylphosphine 124 mol% in acetonitrile at 30 gives 4-bromoindole in 86% yield fEq 10 62 Several functional groups, such as esters, ethers, bromides, tnflates, and additional nitro groups, have been shown to be compatible with the reaction conditions... 

Chiral phosphinous amides have been found to act as catalysts in enantio-selective allylic alkylation. Horoi has reported that the palladium-catalyzed reaction of ( )-l,3-diphenyl-2-propenyl acetate with the sodium enolate of dimethyl malonate in the presence of [PdCl(7i-allyl)]2 and the chiral ligands 45 gave 46 in 51-94% yields and up to 97% ee (Scheme 38). It is notorious that when the reaction is carried out with the chiral phosphinous amide (S)-45a, the product is also of (S) configuration, whereas by using (R)-45b the enantiomeric (R) product is obtained [165]. 

The discussion of the activation of bonds containing a group 15 element is continued in chapter five. D.K. Wicht and D.S. Glueck discuss the addition of phosphines, R2P-H, phosphites, (R0)2P(=0)H, and phosphine oxides R2P(=0)H to unsaturated substrates. Although the addition of P-H bonds can be sometimes achieved directly, the transition metal-catalyzed reaction is usually faster and may proceed with a different stereochemistry. As in hydrosilylations, palladium and platinum complexes are frequently employed as catalyst precursors for P-H additions to unsaturated hydrocarbons, but (chiral) lanthanide complexes were used with great success for the (enantioselective) addition to heteropolar double bond systems, such as aldehydes and imines whereby pharmaceutically valuable a-hydroxy or a-amino phosphonates were obtained efficiently. 

Chiral phosphine based transition metal complexes are nsed as a powerful tool for asymmetric synthesis (3). A fundamental mechanistic nnderstanding is required for rhodium and mthenium catalyzed reactions. The starting point of those investigations was the clear and detailed stractnral description of the isolated pre catalyst system. 

Phosphine ligands based on the ferrocene backbone are very efficient in many palladium-catalyzed reactions, e.g., cross-coupling reactions,248 Heck reaction,249 amination reaction,250 and enantioselective synthesis.251 A particularly interesting example of an unusual coordination mode of the l,l -bis(diphenylphosphino)ferrocene (dppf) ligand has been reported. Dicationic palladium(II) complexes, such as [(dppf)Pd(PPh3)]2+[BF4 ]2, were shown to contain a palladium-iron bond.252,253 Palladium-iron bonds occur also in monocationic methyl and acylpalladium(II) complexes.254 A palladium-iron interaction is favored by bulky alkyl substituents on phosphorus and a lower electron density at palladium. 

Recently, a further unique domino methodology has been reported by Lu and coworkers (Scheme 2.74) [173]. Herein, a triphenyl phosphine-catalyzed umpolung addition/cyclization of allenes and alkynes containing an electron-withdrawing group 2-316-2-318 followed by reaction with a double nucleophile 2-319 is assumed to account for the production of a broad palette of various heterocycles 2-321 and 2-323 via 2-320 and 2-322, respectively. Dihydrofurans, piperazines, morpholines and diazepanes were obtained during the process. 

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