Aldehydes catalytic allylation

Kondo and Watanabe developed allylations of various types of aldehydes and oximes by using nucleophilic (7r-allyl)ruthenium(ll) complexes of type 154 bearing carbon monoxide ligands (Equation (29)).345 These 73-allyl-ruthenium complexes 154 are ambiphilic reagents and the presence of the carbon monoxide ligands proved to be essential to achieve catalytic allylation reactions. Interestingly, these transformations occur with complete regioselectivity only the more substituted allylic terminus adds to the aldehyde. 

As an alternative approach, chiral Lewis base has been tested for catalytic allylation. Compound 139, reported by Iseki et al.,88 was the first example of a chiral Lewis base that effectively serves as a catalyst in asymmetric allylation in combination with HMPA. Allylation of aliphatic aldehydes with allyl- and crotyltrichlorosilanes in the presence of 139 provides up to 98% ee (Scheme 3-49). 

New catalytic allylation methodologies continue to emerge. For example, iridium-catalyzed transfer hydrogenation of a-(trimethylsilyl)allyl acetate in the presence of aldehydes mediated by isopropanol and employing the iridium catalyst... 

Abstract The purpose of this chapter is to present a survey of the organometallic chemistry and catalysis of rhodium and iridium related to the oxidation of organic substrates that has been developed over the last 5 years, placing special emphasis on reactions or processes involving environmentally friendly oxidants. Iridium-based catalysts appear to be promising candidates for the oxidation of alcohols to aldehydes/ketones as products or as intermediates for heterocyclic compounds or domino reactions. Rhodium complexes seem to be more appropriate for the oxygenation of alkenes. In addition to catalytic allylic and benzylic oxidation of alkenes, recent advances in vinylic oxygenations have been focused on stoichiometric reactions. This review offers an overview of these reactions... 

A simple method for the direct catalytic allylic alkylation of aldehydes and cyclic ketones has been developed.26 The direct catalytic highly chemo- and regio-selective intermolecular a-allyhc alkylation reaction has been mediated by an unprecedented combination of palladium and enamine catalysis which furnishes a-allylic alkylated aldehydes and cyclic ketones in high yield. 

As a conceptually new allylation of aldehydes, an allylic functionality of the homoallyl alcohols is transferred to aldehydes via the formation of a hemiacetal and the elimination of acetone to give a-adduct homoallylic alcohols in the presence of a catalytic amount of Sn(OTf)2 (Equation (107)).274... 

Iridium,204,205 together with osmium, has been not widely used in catalytic hydrogenation. Recently, however, iridium or iridium-based catalysts have been shown to be effective in various hydrogenations, such as in selective hydrogenation of a,P-unsaturated aldehydes to allylic alcohols (Section 5.2), of aromatic nitro compounds to the corresponding hydroxylamines (Section 9.3.6), of halonitrobenzenes to haloanilines without loss of halogen (Section 9.3.2), and in the stereoselective hydrogenation of carbon to carbon double bonds (see, e.g., eqs. 3.25-3.27 and Table... 

It is very well known that jr-allyl palladium complex 1, which is a key intermediate for the Tsuji-Trost type allylation, has an electrophilic character and reacts with nucleophiles to afford the corresponding allylation products. We discovered that bis 7r-allyl palladium complex 2 is nucleophilic and reacts with electophiles such as aldehydes [27] and imines [28-32] (Scheme 2, Structure 2). We have also shown that bis 7r-allyl palladium complex 2 can act as an amphiphilic catalytic allylating agent it reacts with both nucleophilic and electrophilic carbons at once to produce double allylation products [33]. These complexes incorporate two allyl moieties that can bind with different hapticity to palladium (Scheme 3). The different complexes may interconvert by ligand coordination. The complexes 2a, 2b and 2c are called as r]3,r]3-bisallypalladium complex (also called bis-jr-allylpalladium complex), r)l,r)3-bis(allyl)palladium complex, -bis(allyl)palladium complex, respectively. Bis zr-allyl palladium complex 2 can easily be generated by reaction of mono-allylpalladium complex 1 and allylmetal species 3 (Scheme 4) [33-36]. Because of the unique catalytic activities of the bis zr-allyl palladium complex 2, a number of interesting cascade reactions appeared in the literature. The subject of the present chapter is to review some recent synthetic and mechanistic aspects of the interesting palladium catalyzed cascade reactions which in-... 

There are very few examples of Lewis base-promoted allylations of aldehydes with allylstannanes. In 1992 Baba disclosed an intriguing method for allylation of aldehydes with allyl- and 2-butenyltributylstannanes in the presence of catalytic-amounts of dibutyltin dichloride and certain coactivators such as tetrabutylammo-nium iodide, tributylphosphine oxide, HMPA or tetraphenylphosphonium iodide [76]. No definitive mechanistic information is available on the role of the co-activators the authors speculate that the ligands accelerate the metathesis to form allyldibutyltin chloride which is the actual nucleophile. The same group has recently reported the use of a lead(II) iodide/HMPA catalyst for the allylation of a,yff-epoxyketones [76bj. 

The allylation reactions of carbonyl compounds catalyzed by chiral Lewis acids represent a powerful new direction in allylmetal chemistry. Yamamoto and coworkers reported the first example of the catalytic enantioselective allylation reaction in 1991, using the chiral (acyloxy)borane (CAB) catalyst system (see below) [288]. Since then, several additional reports of the catalytic allylation reaction have appeared. To date, the most effective catalyst systems reported for the enantioselective reaction of aldehydes and Type II allyl- and crotylstannane and silane reagents include the Yamamoto CAB catalyst and catalysts complexes composed of various Lewis acidic metals and either the BINOL or BINAP chiral ligands [289-293]. Marshall and Cozzi have recently reviewed progress in the enantioselective catalytic allylation reaction [294, 295]. 

In their synthesis of the cA-octahydronaphthalene nucleus 471 of superstolide A (Fig. 11 -39), Roush and co-workers demonstrated the use of Keck s original catalytic allylation procedure to effect the diastereoselective conversion of aldehyde 472 to the 1,3-vyn diol 473 (79% yield, selectivity=94 6) (Scheme 11-37) [313]. This transformation constitutes a mismatched reaction since the 3-anti diol is favored under substrate-controlled allylation (see Section 11.3 for a discussion of 1,3-stereo-induction) [93]. 

Using Keck s original catalytic allylation procedure, Danishefsky and co-workers converted aldehyde 474 to the homoallylic alcohol 475 (conditions A, Scheme 11-38, 60% yield, >95% ee) used in their total synthesis of epothilones A and B [314], Asymmetric allylation with a stoichiometric amount of Brown s reagent, [(-)-lpc]2BAll (195), however, was higher yielding and required a shorter reaction time (conditions B, Scheme 11-38, 83% yield, >95% ee). 

The fact that several laboratories have already applied the enantioselective catalytic allylation reaction to the synthesis of complex natural products illustrates the eagerness with which the synthetic community has welcomed this methodology. It is hoped that further efforts to find conditions that promote high enantio- and dia-stereoselectivity and low catalyst loading for a variety of aldehyde substrates will continue in this promising new direction of the allylation reaction. 

Compared with well-established electrophilic it-allylpalladium chemisty, the catalytic asymmetric reaction via umpolung of jt-allylpalladium has received very limited exploration [93]. Zhou and co-workers investigated the Pd-catalyzed asymmetric umpolung allylation reactions of aldehydes [22a, 94], activated ketones [95], and imines [96] by using chiral spiro ligands (5)-18e, (S)-17c, and (5)-17a, respectively. One representative example is that of the Pd/(5)-18e-catalyzed umpolung allylation of aldehydes with allylic alcohols and their derivatives, which provided synthetically useful homoallylic alcohols from readily available allylic alcohols, with high yields and excellent enantioselectivities (Scheme 33). 

Tagliavini and Umani-Ronchi found that chiral BINOL-Zr complex 9 as well as the BINOL-Ti complexes can catalyze the asymmetric allylation of aldehydes with allylic stannanes (Scheme 9) [27]. The chiral Zr catalyst 9 is prepared from (S)-BINOL and commercially available Zr(0 Pr)4 Pr0H. The reaction rate of the catalytic system is high in comparison with that of the BINOL-Ti catalyst 4, however, the Zr-catalyzed allylation reaction is sometimes accompanied by an undesired Meerwein-Ponndorf-Verley type reduction of aldehydes. The Zr complex 9 is appropriate for aromatic aldehydes to obtain high enantiomeric excess, while the Ti complex 4 is favored for aUphatic aldehydes. A chiral amplification phenomenon has, to a small extent, been observed for the chiral Zr complex-catalyzed allylation reaction of benzaldehyde. 

Polymer-bound rhodium clusters were used for catalytic hydrogenations of a,/3-unsaturated aldehydes to allylic alcohols. Amination of chloromethylated polystyrene with 2-(2-(dimethylamino)ethoxy)ethanol gave an amine-functionalized polymer. Using the aminated polystyrene and Rh6(CO)i6 in the presence of H2 and CO or CO and water, various a,/ -unsaturated aldehydes were chemoselectively hydrogenated to give allylic alcohols in high yields, generally >95% conversion and 80-100% selectivity, at 303 K. Under the reaction conditions, a number of anionic clusters form, which can be recovered as ions paired to the ammonium cations of the polymer. Clusters identified by... 

Ruthenium complexes attract recent interest as new promising candidates for efficient, specific and environmentally benign allylation catalysts. It is noticeable that some J7 -allylruthenium(II) complexes have an ambiphilic property in catalysis involving the C-0 bond activation [52]. When allyl carboxylates or carbonates are treated with nucleophilic 1,3-dicarboxylates or electrophilic aldehyde in the presence of Ru complexes, catalytic allylations of nucleophiles or electrophiles take place [53]. In both reactions, J7 -allylruthenium complexes are assumed to be intermediates. Independent synthesis and reactions of the model compounds support this observation (Scheme 3.28). This ambiphilicity of the allylruthenium(II) may arise from the different reactivity of and rf forms in the allylic moiety [54]. 

As discussed above, catalytic allylation with allyltrichlorosilanes 21.5a and its congeners is generally confined to conjugated aldehydes (aromatic, heteroaromatic, and a,(3-unsaturated). The recurring problem of poor efficiency in the allylation of aliphatic aldehydes was resolved with the introduction of novel pseudoenantiomeric cinchona-derived amides 21.36 and 21.37 reported by Zhao and coworkers. These novel catalysts proved highly efficient with both aliphatic and aromatic substrates at ambient temperature, enantioselectivily varying between 90 and 98% enantiomeric excess... 

While the chiral aldehydes or allyl nucleophiles are based on stoichiometric amounts for the control of diastereoselectivity [74, 77], it has been found that catalytic amounts of titanium complexes derived from BINOL can mediate the enantioselective addition of allyl stannanes to aldehydes, giving the homoallyl alcohols high enantioselectivity. Mikami reported that the BINOL-Ti complexes prepared in situ in the presence of 4A molecular sieves (MS) catalyze the carbonyl addition reaction of allyl silanes or stannanes to afford the syn product in high enantiomeric excess [78] (Scheme 14.21). 

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