Phase-transfer catalysis inverse

Although the Wacker-type oxidation of olefins has been applied since the early 1980s, processes involving higher olefins are stiU the subject of investigations due to their poor solubility in water. Particularly interesting in this context is the inverse phase-transfer catalysis using water-soluble host molectdes. Indeed, upon a careful choice of the substituent, these receptor molecules avoid the isomerization into internal olefins or make it possible to perform substrate selective oxidations that cannot be achieved a biphasic medium with conventional transition metal catalysts. 

Parshall, S. D. Ittel, in Homogeneous Catalysis. The Applications and Chemistry cf Catalysis by Soluble Transition Metal Comydexes, 2nd ed., Wiley-Interscience. New York 1992. pp. 138-142. 

in Applied Homogeneous Catalysis with OrganometaUic Compounds (Eds. B. Cornils, W. A. Herrmann), VCH, Weinheim 1996, pp. 374-394. 

Yokota, a. Sakakura, M.Tani, S. Sakaguchi, Y. Ishii, Tetrahedron Lett. 2002, 43, 8887. 

14 (a)C. Lapinte, H. Riviere, Tetrahedron Lett. 1977, 43, 3817 (b) Phillips Petroleum Co. 

---

Oxymercuration/demercuration provides a milder alternative for the conventional acid-catalyzed hydration of alkenes. The reaction also provides the Markovnikov regiochemistry for unsymmetrical alkenes.33 Interestingly, an enantioselective/inverse phase-transfer catalysis (IPTC) reaction for the Markovnikov hydration of double bonds by an oxymercuration-demercuration reaction with cyclodextrins as catalysts was recently reported.34 Relative to the more common phase-transfer... 

Monflier and co-workers recently described a new approach based on the use of chemically modified /3-cyclodextrins to peform efficiently the functionalization of water-insoluble olefins in a two-phase system. These compounds behave as inverse phase transfer catalysis, i.e., they transfer olefins into the aqueous phase via the formation of inclusion complexes.322... 

The term Counter Phase Transfer Catalysis (CPTC) was coined by Okano214,215 to describe biphasic reactions catalysed by water soluble transition metal complexes which involve transport of an organic-soluble reactant into the aqueous phase where the catalytic reaction takes place. Similarly, Mathias and Vaidya564,565 gave the name Inverse Phase Transfer Catalysis to describe this kind of biphasic catalysis which contrasts with classical Phase Transfer Catalysis where the reaction occurs in the organic phase and does not involve formation of micelles.389,564... 

Neutral cyclodextrins have been used as chiral phase-transfer catalysts for an interesting inverse phase-transfer catalysis reaction [50]. The Markovnikovhydration of the double bond by an oxymercuration-demercuration reaction has been demonstrated in the presence of cyclodextrins as chiral phase-transfer catalysts to obtain products in low to moderate enantioselectivity (Scheme 7.16). The mercuric salts are water-soluble, and remain in the aqueous phase, whereas the neutral alkenes prefer an organic phase. A neutral cyclodextrin helps to bring the alkenes into the aqueous phase in a biphasic reaction, and also provides the necessary asymmetric environment. 

Various allylic amines and protected allylic alcohols were tested using different cyclodextrins. Although only low to moderate enantioselectivity was obtained, the method demonstrated for the first time an enantioselective inverse phase-transfer catalysis hydration reaction via an oxymercuration-demercuration process. 

Mathias, L.J. and Vaidya, R.A. (1986) Inverse phase transfer catalysis. First report of a new class of interfacial reactions./. Am. Chem. Soc., 108, 1093. Fife, W.K. and Xin, Y. (1987) Inverse phase-transfer catalysis probing its mechanism with competitive transacylation. J. Am. Chem. Soc., 109, 1278. 

Several concepts have been suggested to increases the rates in aqueous-phase catalytic conversion of higher substrates such as addition of conventional surfactants [3, 5] (cf. Sections 4.5 and 6.1.5), counter (inverse)-phase transfer catalysis using /3-cyclodextrins [6] (cf. Section 4.6.1), addition of promoter ligands, e.g. PPh3 [7], or co-solvents (cf. Section 4.3). However, addition of foreign compounds militates against the facile catalyst separation and purification of the products and increase the costs as well. 

Finally, extraction of the important reactive species can be executed in the opposite direction, from organic phase to water. This is called inverse phase-transfer catalysis. Catalysts for such processes are mostly cyclodextrins or modified derivatives thereof. Relatively few applications of this type of PTC have been published. Whereas the present section is concerned only with the organic phase as the location of the proper chemical reaction, important contributions of inverse PTC toward organometallic catalysis are detailed in Section 4.6.2. 

It is difficult to verify the counter- or inverse-phase transfer catalysis strictly, because the catalyst more or less acts as a surfactant as well as a normal PTC [13]. However, it should be a positive proof of the counter-PTC to ascertain that the aqueous phase is where the products are formed. 

Inverse-phase Transfer Catalysis (cf. Section 4.6.2) has been successfully applied to perform the quantitative and selective oxidation of 1-decene in an aqueous two-phase system [22]. The success of this oxidation is mainly due to the use of /3-cyclodextrin - a cyclic oligosaccharide composed of seven glucopyranose units - functionalized with hydrophilic or lipophilic groups. The best results have been obtained with a multicomponent catalytic system composed of PdS04, H9PV6Mo6O40, CuS04, and per(2,6-di-0-methyl)-/3-cyclodextrin (Eq. 7) [23]. 

Fife, W. C., and Y. Xin, Inverse Phase Transfer Catalysis Probing the Mechanism with Competitive Transacylation, /. Amer. Ghem. Soc., 109, 1278 (1987). 

Mathias,L. J., andR. A. Vaidya, Inverse Phase Transfer Catalysis. First Report of a New Class of Interfacial Reactions, J. Amer. Chern.Soc.,m, 1093 (1986). 

Shimizu, S., Y. Sasaki, and C. Hirai, Inverse Phase Transfer Catalysis. Palladium-Catalyzed Reduction of Bromoanisoles with Sodium Formate, Chem Soc.Jpn.,63,176 (1990). 

Trotta, F., Phthalic Acid Esters Hydrolysis Under Inverse Phase-Transfer Catalysis Conditions, /. Mol. Cat., 85, L265 (1993). 

The Haloform reaction is catalyzed by cyclodextrins in what the authors label as inverse phase transfer catalysis, 25 but the synthetic utility of this variation remains to be seen. An alternative to the use of halogen is a nitroarene catalyzed oxidation of acetophenone with sodium percarbonate or sodium perborate.26 However, the yields of substituted benzoic acids furnished by this method are mediocre (23-73%) in comparison to the conventional Haloform conditions. Likewise, the Haloform reaction of acetone with iodine in liquid ammonia is without synthetic merit (8-12%).27... 

In contrast to the normal and reversed PTC methodologies, in which the chemical transformation takes place in the organic phase, it is reasonable to expect that PTC reactions can also be performed by transferring the organic reactants from the organic phase into the aqueous phase for reaction with a second reactant. Such a complementary methodology is named as inverse phase transfer catalysis (IPTC) by Mathias and Vaidya [124]. Recently, the application of IPTC in organic synthesis has been reviewed by Li et al. [150]. 

FIG. 3 Inverse phase transfer catalysis the dimethylaminop5Tidine-catalyzed reaction of benzoyl chloride and sodium salt of glycine. 

FIG. 5 Inverse phase transfer catalysis Hammett plot for the pyridine 1-oxide-catalyzed reactions of benzoyl chlorides and benzoate ions. 

Mathias. L.J. Vaidya. R.A. Inverse phase transfer catalysis. First report of a new class of interfacial reactions. J. Am. Chern. Soc. 1986. 108. 1093-1091. 

Fife. W.K. Xin. Y. Inverse phase-transfer catalysis Probing its mechanism with competitive transacplation. J. Am. Chem. Soc. 1987. 109, 1278-1279. 

Kuo. C.S. Jwo. J.J. Inverse phase transfer catalysis. Kinetics and mechanism of the pyridine 1-oxide catalyzed substitution reaction of benzoyl chloride and benzoate ion in a two-phase waterldichloromethane medium. J. Org. Chem. 1992. 57, 1991-1995. 

Wang. M.-L. Ou. C.-C. Jwo. J.-J. Study of the reaction of glycine and benzoyl chloride under inverse phase transfer catalysis. Chem. Eng. Commun. 2000, 179. 233-252. 

Boyer. B. Hambardzoumian. A. Roque, J.-P. Beylerian. N. Reaction in biphasic water/organic solvent s>ctem in the presence of surfactant Inverse phase transfer catalysis versus interfacial catalysis. Tetrahedron 1999, 56, 303 307. 

---