Aldehydes allyltributylstannane

Keywords Aldehydes, allyltributylstannane, magnesium iodide etharate, dichloromethane, room temperature, allylation, homoallylic alcohols... 

In 1998, Yamamoto et al. reported the first catalytic enantioselective allylation of imines with allyltributylstannane in the presence of a chiral 7i-allylpalladium complex 23 (Scheme 9) [15]. The imines derived from aromatic aldehydes underwent the allylation with high ee values. Unfortunately, the allylation reaction of aliphatic imines resulted in modest enantioselectivities. They proposed that a bis-Jt-allylpalladium complex is a reactive intermediate for the allylation and reacts with imines as a nucleophile. The bis-Jt-allylpalladium complex seemed the most likely candidate for the Stille coupling [16]. Indeed, the Stille coupling reaction takes place in the presence of triphenylphosphine even if imines are present, whereas the allylation of imines occurs in the absence of the phosphine [17]. They suggested the phosphine ligand played a key role in controlling the... 

It is well-established that 7r-allylpalladium is electrophilic, and no reaction with electrophiles has been observed. However, there is an evidence that bis-7r-allylpalladium (172), generated in situ, could be amphiphilic. Typically, formation of the 2-substituted 3,6-divinylpyran (175) by the reaction of butadiene with aldehyde can be explained by the amphiphilic nature of the bis-7r-allylpalladium 173 generated in situ as an intermediate, which reacts with the electrophilic carbon and the nucleophilic oxygen in the aldehyde as shown by 174 [86]. As a similar reaction, piperidone is obtained by the reaction of butadiene with isocyanate [87]. The reaction of allyltributylstannane (176), allyl chloride and benzalmalononitrile (177) in the presence of PdCl2(Ph3P)2 (3 mol %) afforded the diallylated product 178 in high yield. 

A chiral BINOL-indium(in) complex has been used to catalyse the addition of allyltributylstannane to aldehydes in high ee.184... 

Aldehydes can be allylated with allyltributylstannane using cerium(III) chloride in acetonitrile, a method particularly suitable for substrates bearing acid-sensitive groups.185... 

Carboxylic acids promote the allylation of aldehydes by allyltributylstannane.187 In (g) the case of crotylation, some regioselectivity can be achieved by an appropriate choice of acid. 

The enantioselective addition of allyltributylstannanes to aldehydes and ketones has been performed in the presence of various chiral indium(III) complexes derived from (R)-BINOL,136 (S )-BINOL,137,138 and PYBOX.139,140... 

Another way in which dihydrobenzo[c]furans can be made is by reacting allylic halides having an aldehyde in the same molecule with allyltributylstannane in the presence of a catalytic amount of Pcydba CHClj <02CL158>. 

Corey s asymmetric allylation methodology was utilized in the total synthesis of amphidinolide T3 (95), a marine natural product that exhibits significant antitumor properties37 (Scheme 3.1gg). The asymmetric allylation of the aldehyde 96 was carried out successfully with chiral allylborane reagent generated in situ from allyltributylstannane and (R,R)-82 to furnish the homoallylic alcohol desired (97) in 85% yield with excellent diastereoselectivity. Subsequent conversion of the alcohol to the tosylate ester followed by treatment with potassium hydroxide resulted in formation of the trisubstituted tetrahydrofuran 98. 

Based on this and earlier work, Kobayashi et al. in 1998 reported initial investigations of three-component reactions of aldehydes, anilines and allyltributylstannane to give homoallylic amines 4 [6]. With the catalyst Sc(OT03 in the presence of sodium dodecyl sulfate for building a micellar system, yields in the range 66- 90 % were obtained (Scheme 1). The stability of the catalyst towards oxygen is noteworthy. 

The addition of allyltributylstannane to aldehydes can also be effected with equimolar amounts of MeSiCl3 or MeSiCl(OMe)2 (Eq. 13) [21]. The initial product is the silyl ether which is hydrolyzed in the aqueous work-up. An allylic silane intermediate was shown not to be involved in the addition. The reaction with benzaldehyde could be accomplished with 0.33 equiv. of trichlorosilane but at a much slower rate. The product of this addition was cleaved by treatment with KF or aqueous acetic acid in THE... 

Keck asymmetric allylation The reaction of aldehydes with allyltributylstannane in the presence of Lewis acid catalysts to form homoallylic alcohols. 236... 

Alkylation of carbonyl compounds. The presence of two metallic centers in reagent 1 makes it easy to attain a six-center transition state therefore, much more efficient transfer of an alkyl group to aldehydes is noted. In comparison with the 2,6-dimethylphenoxy (dialkylaluminum) reagents the improvement is remarkable (e.g., 84% vs 0%, 52% vs 10%, the latter seems to be the best case for the mononuclear phenoxide). Contrary to TiCl which promotes ionization of dimethylacetal unit, 1 activates a carbonyl group preferentially toward nucleophiles such as allyltributylstannane and silyl ketene acetals. ... 

While selective reaction of aldehydes takes place with the typical Lewis acids TiCL, SnCl4, TMSOTf, etc., lanthanide triflates [Ln(OTf)3] are unique Lewis acids that change the reaction course dramatically aldimine reacts selectively in the coexistence of aldehydes [70]. Among a series of Ln(OTf)3 tested, Yb(OTf)3 exhibited the most prominent chemoselectivity in addition to high chemical yields. The silyl enol ethers of ketones, allyltributylstannane and Me3SiCN are all applicable as chemoselective nucleophiles (Table 2-9). Preferential formation of Yb(OTf)3-aldimine complexes was postulated by C NMR spectral analysis in the presence of PhCHO and Y-benzylideneaniline. 

Denmark has spectroscopically examined the reaction of both allyl- and 2-bute-nylstannanes with aldehydes using the Lewis acids SnCU and BF3-OEt2 [73, 82]. First, the metathesis of both allyltributylstannane and tetraallyltin with SnCl4 was determined (by C NMR spectroscopy) to be instantaneous at -80 °C. The reaction of allyltributylstannane with a complexed aldehyde was detemiined to be significantly more complicated. When a molar equivalent of SnCU per aldehyde was employed, metathesis was determined to be the preferred pathway for aldehydes. When one half a molar equivalent of SnC per aldehyde is used, the reaction pathways and product distribution become very sensitive to both the aldehyde structure and addition order. A spectrum of mechanistic pathways was documented ranging from direct addition (acetaldehyde) to complete metathesis (pivalalde-hyde) to a competitive addition and metathesis (4-t-butylbenzaldehyde). The results obtained with a molar equivalent of SnCl4 are most relevant, as this reagent stoichiometry is most commonly used in the addition reactions. 

The Lewis acid-promoted addition of allyltributylstannane and ( )-85 to /i-alk-oxy aldehydes has also been investigated [84c]. The Lewis acid-promoted reaction of a 9-siloxy aldehyde 106 with ( )-85 affords almost entirely the syn homo-... 

The addition of allyltributylstannane to a chirally modified aldehyde 111 proceeds in high yield and moderate diastereoselectivity to give the horaoallylic alcohols 112 and 113 (Scheme 10-46) [86]. When the methyl group on the sugar is not present, the reaction proceeds in higher diastereoselectivity (95%) and excellent yield. The formation and reaction of a 2/1 complex (aldehyde/Lewis acid) with the allylstannane can account for the observed selectivity. 

The reaction of methallyltri-n-butylstannane 117 with achiral aldehydes is also effectively promoted by the binol-Ti complex [89 c]. In all but one case (cyclo-hexanecarboxaldehyde), the yields and enantioselectivities observed with the methallylstannane are identical or higher than those obtained in the reactions with allyltributylstannane with only 10 mol% of the binol-Ti complex (Scheme 10-50). Insight into the nature of the titanium catalyst is provided by the observation of asymmetric amplification [89 b] and chiral poisoning [89 g]. An intruiging hypothesis on the origin of enantioselection in allylation and related reactions [89 h]. 

The asymmetric allylation of achiral aldehydes with a novel silver complex has recently been reported (Scheme 10-51) [90]. Initially, it was shown that the silver-promoted reaction of allyltributylstannane with benzaldehyde could be accelerated by triphenylphosphine. A survey of various chiral phosphine reagents and silver salts identified the combination of binap and AgOTf as optimal. The reaction of benzaldehyde and allyltributylstannane promoted by 5 mol% of the binap-AgOTf... 

Chiral rhodium catalyst 118, pioneered by Nishiyama, has been put to use in the addition of allyltributylstannane to achiral aldehydes [91], This catalyst is relatively insensitive to water and can even be purified by silica gel chromatography. The optimized allylation conditions employ 1 equiv of the aldehyde, 1.5 equiv of allyltributylstannane, and 5 mol% of 118 (Scheme 10-53). The reactions with many different aldehydes can all be performed at room temperature to provide good yields of the desired homoallylic alcohols albeit in moderate to poor enan-tioselectivity. 

The reaction of benzaldehyde, aniline, and allyltributylstannane in water was chosen as a model, and several reaction conditions were examined. While the reaction proceeded sluggishly in the presence of either Sc(OTf)3 or SDS, 77% yield of the desired homoallylic amine was obtained in the presence of both Sc(OTf)3 and SDS. It was suggested that an imine formed from the aldehyde and the amine rapidly reacted with allyltributylstannane to afford the desired adduct. 

Table 14-14. Three-component reactions of aldehydes, amine, and allyltributylstannane.

The reachon of y-(trimethylsilyl)allyltributylstannane with aliphatic aldehydes leads to the formahon of 2,6-dialkyl-3,4-dihydropyrans with cis diastereoselechvity (Scheme 8.120) [164]. Aromahc aldehydes did not lead to the cychzahon products. 

The Lewis acid-base complex TiCh-ShPh mediates the Diels-Alder reaction of an acrylate of (,S)-ethyl lactate with cyclopentadiene to afford an endo-adduct with high diastereoselectivity [121]. The same complex is also effective in the allylation of an a-alkoxy aldehyde with allyltributylstannane a homoallyl alcohol is obtained with a high syn selectivity (Scheme 14.53). 

During the past two decades the homogeneous and heterogeneous catalytic enan-hoselective addition of organozinc compounds to aldehydes has attracted much attention because of its potential in the preparation of optically active secondary alcohols [69]. Chiral amino alcohols (such as prolinol) and titanium complexes of chiral diols (such as TADDOL and BINOL) have proved to be very effective chiral catalysts for such reactions. The important early examples included Bolm s flexible chiral pyridyl alcohol-cored dendrimers [70], Seebach s chiral TADDOL-cored Frechet-type dendrimers [28], Yoshida s BINOL-cored Frechet-type dendrimers [71] and Pu s structurally rigid and optically active BlNOL-functionalized dendrimers [72]. All of these dendrimers were used successfully in the asymmetric addition of diethylzinc (or allyltributylstannane) to aldehydes. 

In a related reaction, aqueous allylation of imines has been reported by Bel-luci and co-workers using allyltributylstannane under lanthanide triflate catalysis [130]. Alternatively, the reaction can be performed without catalysis directly with the formaldehyde-generated immonium salts in aqueous media to give, in excellent yields, bis-homoallylamines and tertiary homoallylamines with primary and secondary amines, respectively [131]. These homoallylic amines were also prepared by Sc(OTf)3-catalyzed three-component reactions of aldehydes, amines and allyltributylstannane in micellar systems [132]. 

The catalytic process was also applied to enantioselective additions of meth-allyltributylstannane and allenyltributylstannane to aldehydes [13,14]. The methyl group of methallytin compound does not affect the chemical yield or enantioselectivity in the reaction [13]. A positive nonlinear effect was observed for... 

Functionalized allyltributylstannanes can also be used in the BINOL/Ti-cata-lyzed reaction and addition of P-substituted allyl groups with heteroatoms in the side chain to aldehydes has been achieved with a high degree of enantiocon-trol [ 16]. The catalytic asymmetric allylation has been successfully applied to to -tal syntheses of the macrohdes (l )-(-i-)-ricinelaidic acid lactone and (-)-gloe-osporone [21]. 

Most commonly used chiral Lewis acids have been derived from main group and early transition series elements. An initial attempt at utilizing optically active catalysts of late transition metal complexes for the enantioselective addition of allyltributylstannane to aldehydes was made by Nuss and Rennels [30]. Employment of Rh(COD)[(-)-DIOP]BF4 (11) as a catalyst, however, resulted in only a small degree of asymmetric induction (17% ee). 

Likewise, the competitive reaction of aldehydes 23 and 24 with allyltributylstannane gives homoallylic alcohol (25) exclusively (Scheme 1.18). In contrast, nonfluorinated cycloadduct is produced mainly under the catalysis of BF3 etherate in methylene chloride. These results clearly demonstrate that fluorinated carbonyl compounds are more reactive however, there is a turnabout in the reactivity under the Lewis acid catalytic conditions because of the lower basicity of the carbonyl group than that of the nonfluorinated one. 

Corey and coworkers have described Ae preparation of allylborane (289) by the reaction of bromobo-rane (2W) and allyltributylstannane and shown that (289) undergoes highly stereoselective reactions with )x>th achiral (95-97% ee) and chiral aldehydes (Scheme 54). The corresponding methallyl, ( )-crotyl and 2-chloro- and 2-bromo-allyl reagents were prepared by similar methods and shown to give excellent results in reactions with achiral aldehydes (84-99% ee in most cases). 

Addition of allyltributylstannane to aldehydes is also catalyzed hy Cul in DMF at room temperature. ... 

Allylation. Triflic acid is capable of catalyzing the reaction of allyltributylstannane with aldehydes (not ketones) in water. 

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