Phase transfer catalyzed generation of the (.eta.5-cyclopentadienyl)tricarbonylhydridovanadate anion. Applications to the reduction of halides, sterically encumbered nitro compounds, and the cyclodehydration of .alpha.,.beta.-unsaturated ketones

Falicki, S.; Alper, Howard

doi:10.1021/om00102a021

Cited by 19 publications

(3 citation statements)

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“…In this case, an (η 5 -cyclopentadienyl)tricarbonylhydridovanadate anion is generated in situ, and catalyzes the dehalogenation as shown in Scheme 45. 80 A low-valent vanadium species coordinated to diethyl phosphonate or triethyl phosphite is effective for the stereoselective reduction of gem-dibromocyclopropanes 85 to the corresponding monobromocyclopropanes 86. 81 The less hindered bromine atom is reduced almost exclusively.…”

Section: A Dehalogenationmentioning

confidence: 99%

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Vanadium in Modern Organic Synthesis

1997

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Section: A Dehalogenationmentioning

confidence: 99%

“…Phase transfer conditions can be employed for these catalytic reductive transformations. In this case, an (η 5 -cyclopentadienyl)tricarbonylhydridovanadate anion is generated in situ , and catalyzes the dehalogenation as shown in Scheme 45 …”

Section: Reductionmentioning

confidence: 99%

Vanadium in Modern Organic Synthesis

1997

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“…Nitroarenes are reduced to anilines by the combination of a PTC and Fe 3 (CO)i2-NaOH [des Abbayes, 1977a], CpV(CO) 4 -NaOH [Falicki, 1988] or the bimetaUic catalyst (l,5-hexadieneRhCl) 2 / Co 2 (CO) 8 -CO-NaOH [Hashem, 1984]. The actual reducing agents in these reactions may be the carbonylmetal hydride anions.…”

Section: (X*mentioning

confidence: 99%

Phase Transfer Reactions

Ho¹

1998

Distinctive Techniques for Organic Synthesis

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Chemical reactions involving two or more molecules usually proceed at higher rates in one phase. However, it is not always feasible or expedient to render some reactions under homogeneous conditions. In such cases the phase transfer technique should be considered. Improvement of reactions by phase transfer catalysis (PTC) represents a breakthrough in chemical technology. Although sporadic reports appeared before the 1960s, consolidation of the concept through a series of publications on the theme of extractive alkylation [Markosza, 1965], a patent describing catalysis of heterogeneous reactions [Starks, 1968], and the observations concerning reactions of quaternary ammonium salts in nonpolar media [Brandstrom, 1969[Brandstrom, , 1972 initiated an avalanche of research in the methodology.While the most common phase transfer technique deals with reactants in two immiscible liquids, its scope encompasses gas-liquid, gas-solid, liquid-solid, and presumably solid-solid systems. In comparison with conventional methods, PTC holds considerable advantages in terms of cost (which avoids expensive anhydrous dipolar aprotic solvents), time, mildness, and simplicity. It is often observed that reactivities and selectivities are enhanced under such conditions.From an electrochemical study [Tan, 1994] of the Williamson ether synthesis under phase transfer catalysis, it is concluded that the role of the catalyst is to establish a Galvani distribution potential difference between the two phases which acts as the driving force for transferring the reactive ions from the aqueous medium to the organic layer.The general features of a typical PTC substitution reaction carried out in a system of organic and aqueous phases specifies reaction taking place in the organic layer. The phase transfer agent is present in catalytic amount and capable of moving one reactant in its resident solvent into that of the other reactant or the interfacial region. Only then the two species can react with reasonable speed. Needless to say that strong agitation is a most crucial to maximize reaction rates.Actually there are two mechanistic models for the PTC reaction. In the Starks extraction mechanism the catalyst is biphilic, thus well qualified by a quaternary ammonium or phosphonium salt, either of which having finite solubility in both phases on account of its charge and organophilicity, capable of ferrying the counter anion from the aqueous phase to the organic layer by the partition phenomenon. The 1 Distinctive Techniques for Organic Synthesis Downloaded from www.worldscientific.com by PURDUE UNIVERSITY on 04/13/15. For personal use only.2 Distinctive Techniques for Organic Synthesis anion generated from reaction will pair with the quaternary onium species and enter the aqueous phase and a second catalytic cycle starts at this point. The interfacial mechanism (proposed by Makosza and modified by Brandstrom and Montanari) describes cases in which the catalyst is highly organophilic and it functions by anion exchange in the interfacial region. In ot...

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