Allylation of aldehydes with allylic

PEG-grafted polystyrene is also well suited for reactions with highly reactive orga-nometallic reagents, provided that the support has been dried. PEG-containing polymers are generally more difficult to dry than pure polystyrene. Cross-linked PEG is stable towards Lewis acids, and can be used for SnCl4-mediated allylations of aldehydes with allyl silanes [21],... 

Compound 127 was exploited as an efficient ligand for Pd-catalyzed enantioselective allylation of aldehydes with allylic alcohols <2005OL2333>. 

In 1996 Yanagisawa, Yamamoto, and their colleagues first reported the asymmetric allylation of aldehydes with allylic stannanes catalyzed by a BINAP silver(I) complex [29]. The chiral phosphine-silver(I) catalyst can be prepared simply by stirring an equimolar mixture of BINAP and silver(I) compound in THF at room tempera-... 

The stereochemical course of the thermally promoted addition of allylic trialkyl-stannanes to aldehydes is dependent upon the geometry of the 2-butenyl unit [67, 69], The reaction is believed to proceed via a cyclic, six-membered, chair-like transition structure. Reaction of an -2-butenylstannane provides the anti homoallylic alcohol, while an Z-2-butenylstannane affords the corresponding syn homoallylic alcohol (Scheme 10-37). The allylation of aldehydes with allylic stannanes has also been performed under high pressure and neutral conditions [70]. The stereochemical outcome of the reaction of E- and Z-2-butenylstannanes with aldehydes under high pressure was almost identical to the results obtained thermally. 

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. 

Mechanistic Aspects of Allylation of Aldehydes with Allylic Stannanes... 

Chiral phosphorarnides, as developed by Denmark during the late 1990s [25], are efficient catalysts for the allylation of aldehydes with allyl trichlorosilane [26a] or the aldol condensation of trichlorosilyl-enol ethers with aldehydes [26b]. However, the first example of supported chiral phosphorarnides on a polymeric matrix was reported only in 2005 [27]. 

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. 

Allylations of aldehydes and imines also constitute important carbon-carbon bond-forming reactions [14]. A range of metal-based Lewis acid catalysts have been reported. Hall and co-workers described the Bronsted acid-catalyzed allylation of aldehydes with allyl boronate (Equation 10.8) [15]. 

Tab. 3 Biphasic allylation of aldehydes with allyl compounds and SnCI2.

Allylation. TaCls is useful for promoting allylation of aldehydes with allyl-trimethylsilane as well as acetylation of alcohols, therefore these two reactions can be achieved without isolation of the homoallylic alcohols. 

Allylation of aldehydes with allyl alcohols. Umpolung of allylic alcohols (e.g., isoprenol) and the direct nucleophilic attack on aldehydes is realized in the presence of (PhCN)2PdCl2 and SnCh. 

The kinetic esters 272 were transformed under reflux in toluene or by acid catalysis into the thermod)mamic isomeric esters 273 that were then oxidized and the resulting bipyridyl dioxides were hydrolyzed to yield optically pure (R)-274. (R) and (S)-274 were highly efficient catalysts for the asymmetric allylation of aldehydes with allyl(trichloro) silanes (03JOC6329). 

Related Sc(OTf)3-catalyzed allylation of aldehydes with allyl-tributyltin in nitromethane, allylation of aldehydes with allyl-germanes, allylation of acylsilanes, and intramolecular allenylation of propargyl silanes have also been reported. The allylation of aldehydes with tetraallyltin proceeds smoothly in micellar systems without using any organic solvents. Novel allylation of aldehydes with alkeneylepoxides is catalyzed by Sc(OTf)3 to produce 5-hydroxy-a, 8-unsaturated aldehydes. ... 

Nucleophilic allylation of aldehydes with allyl alcohol proceeds smoothly in the presence of Et2Zn via the formation of nucleophilic allylethylzinc 327 to provide the homoallyl alcohol 328 [120],... 

Reinvestigation of Fluoride-Catalyzed Allylation of Aldehydes with Allyl-... 

Scheme 10.17 Reductive allylation of aldehydes with allylic carbonates.

Table 16.7 Cr catalyzed allylation of aldehydes with allyl tin (103)...

Catalytic enantioselective protonation of prochiral ketone enolates is a beneficial route to optically active carbonyl compounds possessing a tertiary asymmetric carbon at the a-position. In the asymmetric protonation of trimethylsilyl enolates with methanol, BINAP-AgF has been found to act as a chiral catalyst [90,91], which is also known to catalyze asymmetric allylation of aldehydes with allylic trimethoxysilanes [42] as well as asymmetric aldol reaction with trimethoxysilyl enolates [54]. This protonation can be most effectively performed using 6 mol% ofBINAP and 10 mol% of... 

Shimida T, Kina A, Hayashi T (2003) A new synthetic route to enantiomerically pure axially chiral 2,2 -bipyridine N,N -dioxides. Highly efficient catalysts for asymmetric allylation of aldehydes with allyl(trichloro)silanes. J Org Chem 68 6329-6337... 

Facing these difficulties concerning the syrJanti-selectivity in carbonyl allylations, Marton et al., (1996a) extensively studied the zinc-mediated allylation of aldehydes with allyl halides in cosolvent/HaO (NH4CI) and in cosol-vent/H20 (NH4Cl)/haloorganotin media. The stereochemistry seems to be determined by the structure of the radical anions, which were presumed to be formed through an electron-transfer process. 

Marton, D. Stivanello, D. Tagliavini, G. (1996a) Stereochemical study of the allylation of aldehydes with allyl halides in cosolvent/water(salt)/Zn/haloorganotin media, J. Org. Chem., 61, 2731-7. 

Uneyama, K. Kamaki, N. Moriya, A. Torii, S. (1985) Sn(ii)-Al-promoted allylation of aldehydes with allyl chloride in an aqueous solvent system, J. Org. Chem., 50, 5396-9. 

Liu and Guo et al developed the SnCU-mediated allylation of aldehydes with allyl halides in fully aqueous media with the assistance of co-catalysts, such as TiCU, CuCU, and PdCU [59]. This reaction proceeds in a high regio- and diastereoselective manner therefore, satisfactory yields of the desired anti-y-homoallylic alcohols are obtained (Scheme 10.34). 

Another breakthrough came from Antilla et al., who employed a chiral phosphoric acid as an efficient catalyst for the reduction of prochiral ketones (83). As an extension of their success in the enantioselective allylation of aldehydes with allyl borate [84], they hypothesized that a chiral phosphoric could activate and direct the borane reduction of ketones. Initial studies showed that the asymmetric reduction truly works and, after screening various chiral phosphoric acids, found that 6 stands out as the most suitable catalyst. The enantioselectivity is further improved by using 4-(dimethylamino)pyridine (DMAP) as an additive (ee up to 95%) (Scheme 32.30). To gain mechanistic insight into this reduction, the authors performed several parallel B NMR experiments the results suggest that the complex formed between 6, catechol borate, and DMAP might be the real catalyst for the asymmetric reduction. 

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