Benzaldehydes allylation

This is a black, hydrous mixture of higher oxides of nickel made by treating nickel sulfate in alkaline solution with sodium hypochlorite. In alkaline solution, saturated aliphatic primary alcohols of adequate water-solubility are oxidized to the carboxylic acids (30°, 3-5 hrs.). Benzyl alcohol is oxidized by the alkaline reagent to benzoic acid, but with benzene as solvent and a slight excess of nickel peroxide it is oxidized to benzaldehyde. Allylic alcohols also can be oxidized to aldehydes by this method. 

In a typical example, using a platinum foil cathode, benzaldehyde, allyl bromide, tin powder and cyclohexene, dissolved in a 4 1 mixture of methanol and methanoic acid, were electrolyzed at 50-55 °C, affording the expected product in 91% yield ... 

Aldehydes can also be prepared by the carbonylation of aryl and alkenyl halides and triflate, and benzyl and allyl chlorides using tin hydride as a hydride source and Pd(PhjP)4 as a catalyst[377]. Hydrosilancs arc used as another hydride source[378]. The arenediazonium tetralluoroborate 515 is converted into a benzaldehyde derivative rapidly in a good yield by using Et ,SiH or PH MS as the hydride source[379]. 

Van Leusen and Possel described the use of mono-substituted tosylmethyl isocyanides (TosCHRN=C R = alkyl, benzyl, allyl) in the synthesis of 4,5-substituted oxazoles. For example, 4-ethyl-5-phenyloxazole (8) was prepared in 82% yield by refluxing a-tosylpropyl isocyanide (7) and benzaldehyde for 1 hr with 1.5 equivalent of K2CO3 in MeOH. 

The synthesis of the right-wing sector, compound 4, commences with the prochiral diol 26 (see Scheme 4). The latter substance is known and can be conveniently prepared in two steps from diethyl malonate via C-allylation, followed by reduction of the two ethoxy-carbonyl functions. Exposure of 26 to benzaldehyde and a catalytic amount of camphorsulfonic acid (CSA) under dehydrating conditions accomplishes the simultaneous protection of both hydroxyl groups in the form of a benzylidene acetal (see intermediate 32, Scheme 4). Interestingly, when benzylidene acetal 32 is treated with lithium aluminum hydride and aluminum trichloride (1 4) in ether at 25 °C, a Lewis acid induced reduction takes place to give... 

The titanium complex 4, prepared from (A./ )-2,3-0-isopropylidenc-1,1.4,4-tetraphenyl-1,2,3,4-butanetetrol7,113 and chlorotriisopropoxytitanium or tetraisopropoxytitanium, is treated with 2-propenylmagnesium bromide. The resulting titanate affords, with benzaldehyde, ( —)-(5)-l-phenyl-3-butenol. Several further attempts, which do not include allylation, have also been reported113, as have examples using the dichloride114. 

The reaction of the anion of an aryl allyl sulfoxide with benzaldehyde can take place via an a or y attack. The a attack leads to a product with three stercogcnic centers (four possible diastereomers) whereas the y attack results in a product which has only two stereogenie centers and geometric isomerism is possible. 

Addition of the anions of allyl aryl sulphoxides 407 to benzaldehyde proceeds readily and affords a mixture of products resulting from both a- and y-attack of the allyl anion483 (equation 240). In the case of the a-attack a mixture of all four possible diastereoisomers is observed, while in the case of the y-attack, the diastereoisomer ratio exceeds 2 1. 

Allylboronates are attractive reagents for the highly diastereoselective ally-lation of carbonyl compounds. A sequential cross-metathesis-allylation reaction has recently been developed by Grubbs et al. [88c] and by Miyaura et al. [103]. The sequence is illustrated in Scheme 23 for the formation of homoallylic alcohol 114 from allylboronate 112, acetal 113, and benzaldehyde [88c]. 

Methoxy-benzaldehyd s.S. 286, 406). Aryl-benzyl- sowie Vinyl- und Allyl-aryl-ather werden durch gemischte Hydride aus Lithiumalanat/Obergangsmetall-Salzen (z.B. Nickelchlorid) reduktiv gespalten1,2. 

Other examples that involve intermediate allyl cations are illustrated in Scheme 1.4. The cationic palladium(II) complex [Pd(dppp)(PhCN)2](BF4)2 coordinates the carbonyl oxygen of benzaldehyde and the activated carbonyl carbon attacks the isoprene, forming the allyl cation 10 which then cyclizes to give the 4-methyl-6-phenyl-5,6-dihydro-2H-pyran [22]. 2-Oxopropyl acrylate 11, in the presence of trimethylsilyltrifluoromethane sulfonate (TMSOTf) and methoxytrimethylsilane (MeOSMT), generates the cation 11a which is an efficient dienophile that reacts easily with the cyclohexadiene to give the Diels-Alder adduct in good yield [23]. 

A family of interesting polycychc systems 106 related to pyrrolidines was obtained in a one-pot double intermolecular 1,3-dipolar cycloaddition, irradiating derivatives of o-allyl-sahcylaldehydes with microwaves in toluene for 10 min in presence of the TEA salt of glycine esters [71]. A very similar approach was previously proposed by Bashiardes and co-workers to obtain a one-pot multicomponent synthesis of benzopyrano-pyrrolidines 107 and pyrrole products 108 (Scheme 37). The latter cycloadducts were obtained when o-propargylic benzaldehydes were utihzed instead of o-allyhc benzalde-hydes, followed by in situ oxidation [72]. 

Benzaldehyde dimethyl acetal 121 reacts, for example, with the silylated allylic alcohol 645, in the presence of SnCl2-MeCOCl, via an intermediate analogous to 641, to the 3-methylenetetrahydrofuran 646 and methoxytrimethylsilane 13 a [182], whereas benzaldehyde dimethyl acetal 121 reacts with the silylated homoallylalco-hol 640 in the presence of TMSOTf 20 to afford exclusively the ds 4-vinyltetrahy-drofuran 647 and 13 a [183]. A related cyclization of an a-acetoxy urethane 648 containing an allyltrimethylsilane moiety gives the 3-vinylpyrrohdine 649 in 88% yield and trimethylsilyl acetate 142 [184, 185]. Likewise, methyl 2-formylamido-2-trimethylsilyloxypropionate reacts with allyltrimethylsilane 82 or other allyltri-methylsilanes to give methyl 2-formamido-2-aUyl-propionate and some d -unsatu-rated amino acid esters and HMDSO 7 [186] (Scheme 5.56). 

The formation of ethers such as 1806 by EtsSiH 84b can also be catalyzed by trityl perchlorate to convert, e.g., benzaldehyde in 84% yield into dibenzyl ether 1817 [48]. The combination of methyl phenethyl ketone 1813 with O-silylated 3-phenyl-n-pro-panol 1818, in the presence of trityl perchlorate, leads to the mixed ether 1819 in 68% yield [48] (Scheme 12.15). Instead of trityl perchlorate, the combination of trityl chloride with MesSiH 84a or EtsSiH 84b and sodium tetrakis[3,5-bis-(trifluoro-methyl)phenyl]borane as catalyst reduces carbonyl groups to ethers or olefins [49]. Employing TMSOTf 20 as catalyst gives very high yields of ethers. Thus benzaldehyde reacts with O-silylated allyl alcohol or O-silylated cyclohexanol to give the... 

Deprotonation of allylic aryl sulfoxides leads to allylic carbanions which react with aldehyde electrophiles at the carbon atom a and also y to sulfur . With benzaldehyde at — 10 °C y-alkylation predominates , whereas with aliphatic aldehydes at — 78 °C in the presence of HMPA a-alkylation predominates . When the a-alkylated products, which themselves are allylic sulfoxides, undergo 2,3-sigmatropic rearrangement, the rearranged compounds (i.e., allylic sulfenate esters) can be trapped with thiophiles to produce overall ( )-l,4-dihydroxyalkenes (equation 24). When a-substituted aldehydes are used as electrophiles, formation of syn-diols 27 occurs in 40-67% yields with diastereoselectivities ranging from 2-28 1 (equation 24) . ... 

Mediated by Tin. In 1983, Nokami et al. observed an acceleration of the reaction rate during the allylation of carbonyl compounds with diallyltin dibromide in ether through the addition of water to the reaction mixture.74 In one case, by the use of a 1 1 mixture of ether/water as solvent, benzaldehyde was allylated in 75% yield in 1.5 h, while the same reaction gave only less than 50% yield in a variety of other organic solvents such as ether, benzene, or ethyl acetate, even after a reaction time of 10 h. The reaction was equally successful with a combination of allyl bromide, tin metal, and a catalytic amount of hydrobromic acid. In the latter case, the addition of metallic aluminum powder or foil to the reaction mixture dramatically improved the yield of the product. The use of allyl chloride for such a reaction,... 

Mg. Li and co-worker first reported magnesium-mediated Barbier-Grignard allylation of benzaldehyde in water (Eq. 8.73).172 Recently, a study was completed in which some water-tolerant allylating agents were prepared in situ from allylmagnesium chloride and various metallic salts reacted with aldehydes in THF-FLO to afford the desired homoallylic alcohols.173... 

Indium(I) iodide serves as a two electron reducing agent to promote a Ni-catalyzed allylation of benzaldehyde with 1,3-dienes [23]. In the presence of a catalytic amount of Ni(acac)2 and a stoichiometric amount of Ini, 1,3-butadiene reacts with 2 equiv. of benzaldehyde to provide a mixture of a 1,4-diol 28 and 1,6-diol 29 and/or with 1 equiv. of benzaldehyde to give 27 (Eq. 8). The product distribution of 27-29 markedly depends on the solvent, the ligand, and the additive employed (Table 2). The combination of Ni(acac)2, PPI13, and 3 equiv. of water in DMI provides the 1,4-diol 28 as the major product (run 1). Under similar conditions, dppb dramatically changed the reaction course and the mono-allylation product 27 is produced exclusively (run 2). In contrast to these, the reaction in dry THF provides the 1,6-diol 29 in excellent yield (rim 3). 

Table 2 Ni-catalyzed, Ini-mediated allylation of benzaldehyde with 1,3-butadiene...

Another advantage of the Et2Zn-Ni catalysis over the Et3B-Ni catalysis is that only the former can promote the reductive coupling of 1,3-cyclohexadiene with aldehydes (c.f., run 8, Table 3). For example, under the Et2Zn-Ni catalysis, 1,3-cyclohexadiene smoothly reacts with benzaldehyde at room temperature and provides 53 in 61% isolated yield (Scheme 13). Curiously, however, the product 53 is not the expected homoallylation product, but an allylation product. 

Scheme 13 Ni-catalyzed allylation (not homoallylation) of benzaldehyde with 1,3-cyclohexadiene promoted by Et2Zn...

As shown in Scheme 2.20, selective lithiation of substrate 2-87 by treatment with LDA in THF at -78 °C triggers an intramolecular Michael/intermolecular aldol addition process with benzaldehyde to give a mixture of diastereomers 2-90 and 2-91. 2-91 was afterwards transformed into 2-92, which is used as a chiral ligand for Pd-catalyzed asymmetric allylic substitution reactions [29]. 

Zr compounds are also useful as Lewis acids for oxidation and reduction reactions. Cp2ZrH2 or Cp2Zr(0 Pr)2 catalyze the Meerwein-Ponndorf-Verley-type reduction and Oppenauer-type oxidation simultaneously in the presence of an allylic alcohol and benzaldehyde (Scheme 40).170 Zr(C)1 Bu)4 in the presence of excess l-(4-dimethylaminophenyl) ethanol is also an effective catalyst for the Meerwein-Ponndorf-Verley-type reduction.1 1 Similarly, Zr(0R)4 catalyze Oppenauer-type oxidation from benzylic alcohols to aldehydes or ketones in the presence of hydroperoxide.172,173... 

Figure 6.25. Asymmetric allylation of benzaldehyde catalysed by a fluorinated Ti/BINOL complex under...

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