Zn-Catalyzed Asymmetric Allylation for the Synthesis of Optically Active Allylglycine Derivatives. Regio- and Stereoselective Formal α-Addition of Allylboronates to Hydrazono Esters

Abstract

We have developed Zn-catalyzed asymmetric allylation of hydrazono esters with allylboronates. The reactions proceeded smoothly in high yields and high stereoselectivities. Remarkably, formal α-addition occurred for α-substituted allylboronates exclusively, and excellent stereoselectivities were observed. This is the first example of catalytic regio- and stereoselective allylations with formal α-addition. In addition, the reaction proceeded in aqueous media, and the use of water is essential. Zn(OH)2 might be a catalyst in this asymmetric allylation, and the catalytic activity of Zn(OH)2 was confirmed. This is also the first case of chiral metal hydroxide-catalyzed asymmetric reactions.

Chiral Zinc‐Catalyzed Asymmetric α‐Alkylallylation and α‐Chloroallylation of Aldehydes

“…[5b,e-i, 6f, 7] Recently, we found that allylation reactions of allylboronates with aldehydes proceed smoothly in the presence of catalytic amounts of Zn(OH) 2 and 2,9-dimethyl-1,10-phenanthroline (dmp) in aqueous media. [8] When a-substituted allylboronates such as 2 a were employed, the a-addition products were obtained exclusively with syn selectivities.…”

“…[8] A key species is assumed to be gsubstituted allylzinc with chiral ligand 4, [12] which can react smoothly with aldehydes in a g-addition fashion. A kinetic investigation revealed a first-order dependence on the concentration of allylboronate and a zero-order dependence on the concentration of electrophile.…”

“…Furthermore, a-addition is a rare case of asymmetric allylation with allylboron reagents. [8,20] It is noted that optically active boron reagents 2 [21] are not needed, and that racemic 2 and a catalytic amount of a chiral source efficiently gave optically active homoallylic alcohols with neighboring stereogenic centers. [12] Although direct observation of the allylzinc species with chiral ligand 4 has not yet been successful, we could detect some allylzinc species with dmp by ESI mass spectrometry.…”

Atom-Economic Synthesis of 4-Pyrones from Diynones and Water

“…Generally, water offers several "green chemistry" benefits as a solvent in organic transformations, including high efficiency, lower cost, ease of process, green and environmental protection [3,4]. Recently, there are many reports of clean transformations in water medium [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], such as coupling reactions [20][21][22][23][24][25][26][27][28][29][30], cyclizations [31][32][33][34], Michael additions [35][36][37][38][39], and condensations [40,41]. Additionally, H2O also participates in organic reactions as a nucleophile [42,43] to provide various kinds of functional compounds such as imidazo [1,2-a]pyridines [44], amino acid salts [45], α-amino ketones [46], and 1,3-oxazinan-2-ones [47]…”

Copper(II) and Bismuth(III) Hydroxide Catalyzed Addition Reactions of Hydrazonoester with Allenylboronate in Aqueous Media

“…[2][3][4] Recently, we were the first to report that allylboronates react with hydrazonoesters in aqueous media in the presence of zinc hydroxide [Zn(OH) 2 ] chiral diamine complex to afford allylglycine derivatives in high yields with high enantioselectivities. 5 We also described Zn(OH) 2 -catalyzed allylation reactions of aldehydes with allylboronates in aqueous media. 6 We further investigated other metal hydroxides and found that several metal hydroxides worked well as catalysts in aqueous media.…”