Allyl alcohols homogeneous catalysis

However, styrene and cyclohexene gave complex product mixtures, and 1-octene did not react under the same reaction conditions. Thus, the activity of this catalyst is intrinsically low. Jacobs and co-workers [159,160] applied Veturello s catalyst [PO WCKOj ]3- (tethered on a commercial nitrate-form resin with alkylammonium cations) to the epoxidation of allylic alcohols and terpenes. The regio- and diastereoselectivity of the parent homogeneous catalysts were preserved in the supported catalyst. For bulky alkenes, the reactivity of the POM catalyst was superior to that of Ti-based catalysts with large pore sizes such as Ti-p and Ti-MCM-48. The catalytic activity of the recycled catalyst was completely maintained after several cycles and the filtrate was catalytically inactive, indicating that the observed catalysis is truly heterogeneous in nature. 

The involvement of transition-metal allenylidene complexes in homogeneous catalysis was reported for the first time by B. M. Trost and co-workers in 1992 (Scheme 35) [293-295]. The catalytic reactions allowed the preparation of a wide variety of tetrahydropyranyl and furanyl p,y-unsaturated ketones starting from hydroxy-functionalized alkynols and allylic alcohols, the key step in the catalytic... 

Kuntz, E., Amgoune, A., Lucas, C. and Godard, G. (2006) Palladium TPPTS catalyst in water C-allylation of phenol and guaiacol with allyl alcohol and novel isomerisation of allyl ethers of phenol and guaiacol./. Mol. Catal. A Chem., 244,124. Kuntz, E.G. (1987) Homogeneous catalysis. .. in water. Chemtech, 17, 570. Cornils, B. (1999) Bulk and fine chemicals via aqueous biphasic catalysis. /. Mol. Catal. A Chem., 143, 1. 

To overcome a main problem eissociaied with homogeneous catalysis, i.e. the recovery of the catalyst, the latest development in this field comprises the functionalization of catalyst precursor 1—3 with perfluoroalkyl chains to enable catalysis to be carried out in an txganic/perfluorinated two-phase solvent system. It has been demonstrated that this approach allows reuse of the catalyst several times. Recently, an elegant synthetic route towards the enantioselective synthesis of chiral allylic alcohols in which... 

Indeed, one can easily conclude that selective allylic oxidation of olefins, in the context of fine chemicals, is a largely underdeveloped area of catalysis. Selenium dioxide catalyzes the allylic oxidation of a variety of olefins with TBHP, affording the corresponding allylic alcohols, but the system is homogeneous [3] and, hence, falls outside the scope of this book. The only heterogeneous catalysts for allylic oxidation which seem to have synthetic utility are palladium-based [4]. 

Direct air epoxidation of propylene to propylene oxide suffers from selectivity problems. Epoxidation by alkyl hydroperoxide, as practiced by Arco, is based on the use of Mo(CO)g as a homogeneous catalyst. The most impressive use of homogeneous catalysis in epoxidation, however, is in the Sharpless asymmetric oxidation of allylic alcohols. In view of its importance, this enantioselective reaction is included in Chapter 9 which is devoted mainly to asymmetric catalysis. 

Note at the outset that asymmetric catalysis in the synthesis of fine chemicals is rarely a single-step process that converts a reactant directly to the final product. It is usually one of the steps in a total synthesis but is often the key step. Hence the analysis of the overall yield will be based on the methods described in Chapter 5. There are many types of reactions where asymmetric catalysis can be applied. The most important of these are C-C bond-forming reactions such as alkylation or nucleophilic addition, oxidation, reduction, isomerization, Diels-Alder reaction, Michael addition, deracemization, and Sharpless expoxidation (of allyl alcohols). A few representative examples (homogeneous and heterogeneous) are given in Table 9.6. 

Libraries of a similar size were used for screening of homogenous catalysis under multiphase conditions and for the extraction of kinetic data for the asymmetric syntheses, thereby increasing the depth of information that was gathered. Steric, solubility, and electronic effects on reactivity were monitored for a substrate library for the isomerization of allyl alcohol derivatives conducted under liquid-liquid conditions. 

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