Allylic alcohols, phase-transfer catalysis

Heteropoly acids can be synergistically combined with phase-transfer catalysis in the so-called Ishii-Venturello chemistry for oxidation reactions such as oxidation of alcohols, allyl alcohols, alkenes, alkynes, P-unsaturated acids, vic-diols, phenol, and amines with hydrogen peroxide (Mizuno et al., 1994). Recent examples include the epoxidations of alkyl undecylenates (Yadav and Satoskar, 1997) and. styrene (Yadav and Pujari, 2000). 

Lygo, B. and To, D.C.M., Asymmetric Epoxidation via Phase-transfer Catalysis Direct Conversion of Allylic Alcohols into a, -Epoxyketones. Chem. Commun. 2002, 2360-2361. 

Phase-transfer catalysis has been developed by the combination of Keggin-type heteropolyanions and quaternary countercations such as tetrahexyl-ammonium or cetylpyridinium ion. The oxidations of alcohols (306), allyl alcohols (307), olefins (308), alkynes (309), /J-unsaturated acids (310), v/ c-diols (311), phenol (312), and amines (313) are the examples. 

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. 

Cyclic allylic alcohols fairly easily cycloadd dichlorocarbene, particularly if generated under chloroform/base/phase-transfer catalyst conditions. Five- and six-membered-ring allylic alcohols form a mixture of cis- and fran.v-isomers, while those of larger rings form only the trans-isomer. In contrast with the phase-transfer catalysis method, dichlorocarbene generated from bromodichloromethyl(phenyl)mercury did not add to cyclohex-3-en-1 -ol, while cyclonon-3-en-l-ol yielded exo-10,10-dichlorobicyclo[7.1.0]decan-2-ol (28 /o), which could not be purified. Examples of dichlorocarbene adducts to cyclic allylic alcohols are presented in Table 19. 

Ishii, Y., Yamawaki, K., Ura, T., et al. (1988). Hydrogen Peroxide Oxidation Catalyzed by Heteropoly Acids Combined with Cetylpyridinium Chloride. Epoxidation of Olefins And Allylic Alcohols, Ketonization of Alcohols and Diols, and Oxidative Cleavage of 1,2-Diols and Olefins, J. Org. Chem., 53, pp. 3587-3593 Sato, K., Aoki, M., Ogawa, M., et al. (1997). A Halide-Free Method for Olefin Epoxidation with 30% Hydrogen Peroxide, Bull. Chem. Soc. Jpn., 70, pp. 905-915 Xi, Z. W., Zhou, N., Sun, Y., et al. (2001). Reaction-Controlled Phase-Transfer Catalysis for Propylene Epoxidation to Propylene Oxide, Science, 292, pp. 1139-1141 Neumann, R. 

Phase transfer catalysis is implicated in an improved synthesis of m-1,2-diols by permanganate oxidation of olefins. The regiospecific conversion of allylic alcohols into cw-l,2-diols by oxymercuration has been described (Scheme 144) little regiospecificity is observed when this sequence is applied to acyclic allylic alcohols. 

Re has recently come to the forefront in liquid phase oxidation catalysis, mainly as a result of the discovery of the catalytic properties of the alkyl compound CH3Re03 [methyltrioxorhenium (MTO)]. MTO forms mono-and diperoxo adducts with H2O2 these species are capable of transferring an oxygen atom to almost any nucleophile, including olefins, allylic alcohols, sulfur compounds, amides, and halide ions (9). Moreover, MTO catalysis can be accelerated by coordination of N ligands such as pyridine (379-381). An additional effect of such bases is that they buffer the strong Lewis acidity of MTO in aqueous solutions and therefore protect epoxides, for example. 

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