Catalytic Use of Zinc Amide for Transmetalation with Allylboronates: General and Efficient Catalytic Allylation of Carbonyl Compounds, Imines, and Hydrazones

Abstract

The efficient catalytic allylation of ketones, imines, and hydrazones with allylboronates using a catalytic amount of zinc amide is reported. In this reaction, the boron-to-zinc exchange process occurred smoothly to afford the corresponding allylzinc amides, and the desired allylation reactions proceeded in high efficiency (~0.1 mol%). A mechanistic study revealed that transmetalation was a rate-determining step in the catalytic cycle, and also that the amide ligand on the zinc center played a key role in preparing reactive allylzinc species. Catalytic asymmetric allylations were also investigated, and high enantioselectivities were obtained using chiral di-

Zinc Hydroxide‐Catalyzed Asymmetric Allylation of Acetophenones with Amido‐Functionalized Allylboronate in Water

“…Variety of alkali or alkaline‐earth metal salts were first examined as a water‐soluble additive, but no or only a trace amount of the desired product was observed (Entries 2–5). Then, we employed commercially available zinc, copper, and indium salts with the expectation of activation of the allylboronate (Entries 6–12) . Use of ZnBr 2 , Zn(OTf) 2 , CuI, or CuBr 2 resulted in almost no reaction.…”

“…Then, we employed commercially available zinc, copper, and indium salts with the expectation of activation of the allylboronate (Entries 6-12). [22][23][24][25][26] Use of ZnBr 2 , Zn(OTf) 2 , CuI, or CuBr 2 resulted in almost no reaction. On the other hand, Zn(OMe) 2 and Zn (OH) 2 successfully mediated the desired nucleophilic addition to provide 2 a in 28% and 26% yields, respectively, even though the reactions were carried out in a suspension (Entries 8 and 9).…”

Use of a (β‐Amidoallyl)boronate as a Nucleophilic Reagent in Catalytic Enantioselective Addition to Isatins

“…In contrast, other types of divalent metal reagents such as Mg( n Bu) 2 were ineffective for this reaction and gave comparatively low product yields (21 %; Table , Entry 5). On the basis of these experimental results, Et 2 Zn was considered to be the most effective additive to ensure the efficient and high‐yielding synthesis of 3a …”

Silylative Cyclopropanation of Allyl Phosphates with Silylboronates

“…As a result, two broad peaks at δ =8.4 and 25.0 ppm were observed with the area ratio of 1:1.4. Based on the relevant literature precedents,13b,c, 17 these peaks could be assigned as tetracoordinated anionic boron species 8 and the desilylated three‐coordinate boron species 9 , respectively. The formation of 9 indicates the generation of dimethylphenylsilylpotassium ( 10 ) as the byproduct,18 which could be the active nucleophile in the present cyclopropanation.…”