Allylation of benzaldehyde

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...

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

A symmetric activation is also observed in the combination of (/f)-BINOL and Zr(0 Bu)4, which promotes enantioselective synthesis of homoallylic alcohols (Scheme 8.13). A 2 1 ratio of (/ )-BINOL and Zr(0 Bu)4 without any other chiral source affords the homoallylic alcohol product in 27% ee and 44% yield. Addition of (7 )-(+)-a-methyl-2-naphthalenemethanol ((/ )-MNM) leads to higher enantiomeric excess (53% ee) than those using only (7 )-BINOL. Therefore, (7 )-MNM can act as a chiral activator a higher ee can be achieved via activation of the allylation of benzaldehyde by addition of (7 )-MNM as a product-like activator. 

Eq. 59), and even surprisingly high for aliphatic ketones such as 2-butanone, a substrate that offers very little steric discrimination (Eq. 60). Reagent 74 is less effective than 70 in allylations of aldehydes (e.g., 90% ee vs. >98% ee for 70 in the allylation of benzaldehyde). The superior reactivity and selectivity of 74 with ketones is ascribed in part to the lesser steric bulk of the phenyl substituent compared to the trimethylsilyl unit of reagent 70. The smaller phenyl substituent of 74 would provide a better fit for ketones in the chiral pocket of the reagent. 

Table 18 Ni(n)-catalyzed allylation of benzaldehyde. Reproduced with permission from ACS Publications...

Kobayashi et al. also demonstrated the efficiency of reagent 60 derived from (S)-proline generating asymmetric inductions of up to 88% ee for the catalytic allylation of benzaldehyde [66,67]. 

Tab, 8.11 Indium-mediated palladium-catalyzed allylation of benzaldehyde with allylic compounds... 

The allylation of aldehydes via organotin reagents displays a negative activation volume [76]. As a matter of fact, the allylation of benzaldehyde with diallyltin dibromide is accelerated by addition of water [77]. The reaction was extended to various aldehydes and ketones and to various allylic organotin dichlorides [78] or tet-raallyltin in acidic aqueous medium [79]. With scandium triflate as a catalyst, tet-... 

As well as allylation reactions catalysed by Lewis acids, it has been shown that the reaction can be catalysed by Lewis bases. In 1994, Denmark showed that allylation of benzaldehyde (6.01) with allyltrichlorosilane (6.95) could be achieved using phosphoramide (6.96) as a catalyst. A range of such phosphoramides has... 

Alvarez-IbaiTa. C. Csaky. A.G. Martin. M.El. Quiroga. M.L. Study of the asymmetrie synthesis of (Z)-y-substituted-0(,P-didehydroglutamate.s from V-alkylidene-glycinates. Tetrahedron 1999. 55 (23). 7319-7330. Yanagisawa, A. Yamada. Y. Yamamoto. H. Effect of crown ethers on the regioselectivity of allylation of benzaldehyde with allylic barium reagents. Synlett 1997. (9). 1090-1092. 

Indium metal or indium iodide as a reducing agent can be used for umpol-ung of TT-allylpalladium. Araki reported that allylic indium(III) reagents 333 are generated in situ by reductive transmetallation of r-allylpalladium with indium(I) salts [124]. Based on this reaction, nucleophilic allylation of benzaldehyde with allylic chlorides, alcohols, and esters occurred at room temperature in the presence... 

Scheme 7.33 Enantioselective allylation of benzaldehyde using dendritic ligands 41.

Scheme 7.35 Large-scale asymmetric allylation of benzaldehyde using allyltrimethylsilane.

To address the remarkable ot-substituted effects, the Pd-catalyzed allylation of benzaldehyde with a,p- and p,y-disubstituted allylic benzoates has been investigated. Using MBH adducts as substrates, a-methylene-8-butyrolactones (cis-lVt) were obtained exclusively via Pd-catalyzed allylation and spontaneous... 

---