Allylation of aldehyde

The allylation of aldehydes provides a useful route to homoallylic alcohols. The most popular methods for achieving this in an asymmetric fashion are by the use of metal-based Lewis acid catalysts or using Lewis basic organocatalysts.  

A variety of metal complexes have been investigated as catalysts in this procedure with boron- and titanium-based systems being the most popular. In 1991, H. Yamamoto reported that the allylation of aldehydes with allylsilanes 

MarshaU extended the scope of the reaction to the use of allylstannane reagents, which are more reactive nucleophUes. The addition of triflic anhydride as a promoter overcame a problem with catalyst deactivation and allowed the reaction of allylstarmane (6.79) to take place efficiently and with fairly good stereocontrol in the product (6.80). 

The relatively weaker Lewis acidic titanium complexes require the use of a stronger nucleophile than allylsilanes, and tributylallyltin (6.81) is the most common aUylating agent employed when using titanium-based catalyst systems. In 1993, Umani-Ronchi and Keck published related results using BINOL/titanium derived catalysts. In the Umani-Ronchi system, BINOL is employed, in combination with TiCl2 (0 Pr)2 and shown to work weU with aliphatic 

In an effort to improve catalyst efficiency, Yu and coworkers have shown that it is possible to use molecular accelerators in these reactions. They showed that the addition of the alkylthioborane PrSBEts or the alkylthiotrimethylsilane PrSSiMes allows the use of lower catalyst loadings (typically 1 mol%) in the addition of tributylallyltin to aldehydes. 

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McCluskey et al. have also used [BMIM][BF4] as a solvent for the allylation of aldehydes and Weinreb amides [56]. Similar diastereoselectivities and similar or slightly lower yields were obtained in this ionic liquid, compared with reactions carried... 

The best procedure reported to date for the asymmetric allylation of aldehydes using tributyl(2-propenyl)stannane involves the catalyzed addition with the BINOL-TiCl2 complex as catalyst. Good yields and ee s were obtained for both aromatic and aliphatic aldehydes using 20 mol% of the catalyst127. 

Allylation of aldehydes and ketones by reagents, electrochemically generated at the cadmium anode from allyl bromides, are also known30. 

Table 8. 1-Substituted 3-Butenols from Enantiosclcctive Allylation of Aldehydes by Chiral Titanium Complexes...

Marquez, R, Llebaria, A., Delgado, A. (2001) Studies on the Diastereoselective Allylation of Aldehydes with Enantiopure 2-Sulfinylallyl Building Blocks. Tetrahedron Asymmetry, 12, 1625-1634. 

The first use of chiral sulfoxides as Lewis-base catalysts in the allylation of aldehydes with allyltrichlorosilane was reported in 2003. The formation of the... 

The allylation of aldehydes can be carried out using stannous chloride and catalytic cupric chloride or copper in aqueous media." In-situ probing provides indirect (NMR, CV) and direct (MS) evidence for the copper(I)-catalyzed formation of an allyltrihalostannane intermediate in very high concentration in water (Scheme 8.6). Hydrophilic palladium complex also efficiently catalyzes the allylation of carbonyl compounds with allyl chlorides or allyl alcohols with SnCl2 under aqueous-organic... 

A solid-phase version of the palladium-catalyzed carbonyl allylation of aldehydes by allylic alcohol has been described. Thus, allylation of resin-bound aldehyde (P = Merrifield resin) with allylic alcohols (e.g., MeCH=CHCH2OH) in the presence of SnCl2 afforded the homoal-lylic alcohols under different solvent conditions, in DMSO and aqueous DMSO respectively (Eq. 8.45).102... 

Later, Araki et al. found that the allylation of aldehydes and ketones can be carried out by using catalytic amounts of indium(III) chloride in combination with aluminum or zinc metal.109 This reaction was typically performed in a THF-water (5 2) mixture at room temperature, although the conversion was much slower compared to the same reaction mediated by use of a stoichiometric amount of indium and it required days to complete. When the reaction was carried out in anhydrous THF alone, the yield dropped considerably and side-reactions such as reduction to alcohol increased. The combinations of Al-InCL or Zn-InCl3 gave comparable results. 

Ge. Scandium(III) triflate-catalyzed allylation of carbonyl compounds with tetraallylgermane proceeded readily in aqueous nitromethane to afford homoallyl alcohols in excellent to good yields.175 The presence of H20 is indispensable for the allylation of aldehydes to proceed smoothly. Aldehydes were allylated exclusively in the presence of ketone moieties (Eq. 8.74). 

Pb. Homoallylic alcohols can be obtained from allylation of aldehydes and ketones with allyl bromide promoted by metallic lead in aqueous media.176... 

Allylation of Aldehydes with Dienes Promoted by Trialkylsilanes. 177... 

Intermolecular allylation of aldehydes with 1 -trialkylsilyl-1,3-dienes 22 in the presence of a stoichiometric amount of triethylsilane and a catalytic amount of Ni(cod)2 and PPI13 shows novel regio- and stereoselectivity (Scheme 6) [20-22], When a toluene solution of a 1-silyl-1,3-diene and an aldehyde is refluxed in the presence of trialkylsilane under the catalysis of Ni(cod)2 and PPh3, ( )-allylsilane (E)-23 is obtained exclusively. On the other hand, when the reaction is carried out in THF upon heating at 50 °C as... 

Scheme 8 Plausible reaction mechanism for the Ni-catalyzed mono- and bis-allylation of aldehyde with butadiene, promoted by In(I)I...

Allylation of aldehydes or ketones using allylsilanes, known as the Hosomi-Sakurai reaction, is a useful method for obtaining homoallylic alcohols. TiIV compounds have been successfully applied to this reaction (Scheme 21) 80 Besides aldehydes and ketones, acylsilanes, 0,0-acetals, and A-,(7-acetals can be employed.81-83 1,4-Addition of an allyl group to an a,/ -unsaturated ketone has been also reported.84... 

Pyridine A-oxides have been utilized as asymmetric catalysts in the allylation of aldehydes <06JOC1458> and in the Strecker reaction <06T4071>. In the latter, the chiral A-oxides played a key role in the initial activation of the Si-C bond by coordinating an O atom to the Si atom of silyl cyanide and stabilizing the three-membered complex proposed by the... 

Table 2 Allylation of aldehydes and ketones with allylytterbium bromide...

Allylation of aldehydes accompanying alkoxycarbonylation using cyclopentadienylmolybdenum complexes was also applied to butenolactone synthesis.246,247 Intra- and intermolecular cyclization occurred after allylation of the aldehyde to give a-methylene butenolactone derivatives (Scheme 59). 

Formation of a bis-allylated product of 4-nitrobenzoyl chloride by the reaction with allyltrimethyltin in the presence of a benzylpalladium(ll) complex was observed by Stille and co-workers in 1983.4 Trost and King also reported allylation of aldehydes by allyltin reagents in 1990.456 However, the precise mechanism was unclear until the extended studies were performed by Yamamoto and co-workers since 1995.4S7,4S7a 4S7 Aldehydes and imines react with allyltin reagents in the presence of a palladium catalyst (Equations (95) and (96)), and imines are chemoselectively allylated in the presence of aldehydes (Equation (97)).4S7,4S7l 4 b Mechanistic studies using NMR spectroscopy proved that bis-7t-allylpalladium complex 203 is a key nucleophilic intermediate (Figure 3). 

Platinum-catalyzed allylation of aldehydes with allyltin reagents was first reported in 1995.4S7 457b,483 483a Ar0matiC) aliphatic, a,/3-unsaturated aldehydes and even cyclohexanone undergo allylation with allyltributyltins in the presence of PtClgtPP 113)2 >n THF at room temperature or higher temperature (Equations (123) and (124)). Allylplatinum species are considered to be the active intermediates on the basis of related mechanistic studies on palladium catalysis. 

It is proposed that the reaction proceeds through (i) oxidative addition of a silylstannane to Ni(0) generating (silyl)(stannyl)nickel(n) complex 25, (ii) insertion of 1,3-diene into the nickel-tin bond of 25 giving 7r-allylnickel intermediate 26, (iii) inter- or intramolecular allylation of aldehydic carbonyl group forming alkoxy(silyl)nickel intermediate 27, and (iv) reductive elimination releasing the coupling product (Scheme 69). 

Allylation of aromatic aldehydes with allyl trimethylsilane catalyzed by chiral acyloxyborane gives good results. In contrast, the results are normally poor for aliphatic aldehydes.89 Costa et al.90 introduced another enantioselective allylation procedure aiming to overcome this problem. In the following example, the enantioselective allylation of aldehyde octanal was carried out using... 

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