Allyl alcohols transition metal catalyzed reactions

Transition metal-catalyzed allylic substitution with phenols and alcohols represents a fundamentally important cross-coupling reaction for the construction of allylic ethers, which are ubiquitous in a variety of biologically important molecules [44, 45]. While phenols have proven efficient nucleophiles for a variety of intermolecular allylic etherification reactions, alcohols have proven much more challenging nucleophiles, primarily due to their hard, more basic character. This is exemphfied with secondary and tertiary alcohols, and has undoubtedly limited the synthetic utihty of this transformation. 

A significant part of the examples of transition metal catalyzed formation of five membered heterocycles utilizes a carbon-heteroatom bond forming reaction as the concluding step. The palladium or copper promoted addition of amines or alcohols onto unsaturated bonds (acetylene, olefin, allene or allyl moieties) is a prime example. This chapter summarises all those catalytic transformations, where the five membered ring is formed in the intramolecular connection of a carbon atom and a heteroatom, except for annulation reactions, involving the formation of a carbon-heteroatom bond, which are discussed in Chapter 3.4. 

The transition metal-catalyzed allylation of carbon nucleophiles was a widely used method until Grieco and Pearson discovered LPDE-mediated allylic substitutions in 1992. Grieco investigated substitution reactions of cyclic allyl alcohols with silyl ketene acetals such as Si-1 by use of LPDE solution [95]. The concentration of LPDE seems to be important. For example, the use of 2.0 M LPDE resulted in formation of silyl ether 88 with 86 and 87 in the ratio 2 6.4 1. In contrast, 3.0 m LPDE afforded an excellent yield (90 %) of 86 and 87 (5.8 1), and the less hindered side of the allylic unit is alkylated regioselectively. It is of interest to note that this chemistry is also applicable to cyclopropyl carbinol 89 (Sch. 44). 

Transition metal catalyzed hydrosilylation of a, -unsaturated ketones and aldehydes (78) proceeds in a 1,4- and/or 1,2-fashion to give enol silyl ethers (79) (or the saturated carbonyl compounds 80 after acidic work-up) and/or allyl silyl ethers (81) (or allyl alcohols 82), respectively (equation 54). Monohydrosilanes combined with a Pt or Rh catalyst prefer 1,4-addition. This reaction is an alternative meth for the preparation of enol silyl ethers (79). Diphenylsilane with [RhCl(PPh3)3] catalyst reduces the car-... 

It is generally agreed that Roelen s discovery of the hydroformylation reactiont was the birth of the transition metal-catalyzed carbonylation. Initially, Co catalysts were most extensively used, but the Rh-based processes have since been developed as a superior methods. Although Pd may have been tested along with several other metals, such as Fe, Ru, and Ni, it has never been shown to be very useful in the hydroformylation reaction, sometimes called the oxo process. A publication in 1963 by Tsuji et al. on a related but clearly different reaction of alkenes with CO and alcohols in the presence of a Pd catalyst producing esters was one of the earliesL if not the earliesL reports describing a successful and potentially useful Pd-catalyzed carbonylation reaction. This was soon followed by the discovery of another Pd-catalyzed carbonylation reaction of allylic electrophiles with CO and alcohols ° (Scheme 7). 

Kondo and Mitsudo are the pioneers of transition-metal-catalyzed retro-allylation [7]. They described this phenomenon as deallylation and fi-allyl elimination . Ruthenium-catalyzed reaction of tertiary homoallylic alcohols proceeds in the presence of allyl acetate under an atmosphere of carbon monoxide in tetrahydro-furan (THF) at a relatively high temperature of 180 C to afford the corresponding ketones (Scheme 5.3). Although the exact roles of allyl acetate and carbon monoxide are not clear, they propose a mechanism involving oxidative addition of the... 

The transition-metal-catalyzed substitution reaction of allylic alcohol derivatives with sulfur reagents not only provides the solution to problematic regiochemical outcome, but also offers an opportunity to engineer the stereochemical outcome of reactions. In general, the... 

Lewis acids such as SnCl4 also catalyze the reaction, in which case the species that adds to the alkenes is H2C —O— SnC. Montmorillonite KIO clay containing zinc(IV) has been used to promote the reaction. The reaction can also be catalyzed by peroxides, in which case the mechanism is probably a free-radical one. Other transition metal complexes can be used to form allylic alcohols. A typical example is. ... 

The very first example of the catalytic reductive cyclization of an acetylenic aldehyde involves the use of a late transition metal catalyst. Exposure of alkynal 78a to a catalytic amount of Rh2Co2(CO)12 in the presence of Et3SiH induces highly stereoselective hydrosilylation-cyclization to provide the allylic alcohol 78b.1 8 This rhodium-based catalytic system is applicable to the cyclization of terminal alkynes to form five-membered rings, thus complementing the scope of the titanocene-catalyzed reaction (Scheme 54). 

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