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

Abstract

Metal-hydroxide-catalyzed addition reactions of hydrazonoester with allenylboronate in aqueous media are described. The propargyl adduct was obtained selectively by using copper(II) hydroxide, whereas the allenyl adduct was produced preferentially using bismuth(III) hydroxide in water-DMF (1:3). The reactions proceeded smoothly in pure water without the use of any organic solvents by addition of a small amount (1.7 mol%) of sucrose.The use of water instead of organic solvents is key to attaining the goal of achieving environmentally benign chemical synthesis. Therefore, organic reactions in water are now of great interest and much research effort has been devoted to pursuing efficient reactions in water. 1 Unique reactivity and selectivity have been often observed in aqueous media, but one of the big issues is stability of catalysts in water. Many active catalysts are not stable in water; rather, they decompose in the presence of even a small amount of water. To overcome this, we searched for efficient catalysts that are stable and can work well in aqueous media and found metal hydroxides. With the exception of alkaline and alkaline earth metal hydroxides, these have not been used as catalysts in organic synthesis before our work. 2-4 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. Here we report a convenient method for the synthesis of the allenyl adduct and propargyl adduct of hydrazonoester selectively by using a catalytic amount of metal hydroxide in aqueous media.Functionalized nitrogen-containing allenes and alkynes such as allenic and homopropargylic amines or hydrazines have proved to be versatile intermediates and building blocks. 7 Among the most efficient routes to these compounds are carbon-carbon bond-forming reactions such as the regiospecific addition of propargyl and allenyl metal compounds to C=N electrophiles. [8][9][10][11] We previously reported highly selective preparation of various types of allenic and homopropargylic hydrazines through regiospecific allenylation and propargylation of N-acylhydrazones with propargyl-or allenyltrichlorosilane. 12 The reactions proceeded smoothly under anhydrous conditions using water-sensitive trichlorosilanes. Scheme 1 Addition reactions of hydrazonoester with allenylboronate in aqueous mediaWe first set a reaction of hydrazonoester 1 with allenyl pinacol boronate 2 as a model, and metal hydroxides (20 mol%) were screened as catalysts in H 2 O-DMF (1:3) at room temperature. Among the 18 metal hydroxides tested, we found several that had activities for catalyzing the model reaction. In particular, it was interesting t...

Synthesis of α‐Propargylglycinates Using the Borono‐Mannich Reaction with Pinacol Allenylboronate and Potassium Allenyltrifluoroborate

“…Unlike glyoxylic acid, this substrate cannot form a boronate intermediate through B–O coordination through the carboxyl group and thus the regiochemical outcomes of these reactions would provide important information as to the mechanisms of these reactions using allenylboron reagents. Further, this study could potentially provide a convenient access to ethyl α‐propargylglycinates or ethyl α‐allenylglycinates …”

New trends in bismuth-catalyzed synthetic transformations

“…A convenient method for the synthesis of the allenyl adduct of a hydrazinoester has been reported using allenyl pinacol boronate and bismuth hydroxide as the catalyst. 47 The allenyl vs. propargyl adduct was produced preferentially using Bi(OH) 3 in a water-DMF solvent mixture (Scheme 41).…”

Allylation of Imines and Their Derivatives with Organoboron Reagents: Stereocontrolled Synthesis of Homoallylic Amines

“…Kobayashi and co-workers described the propargylation and allenylation of hydrazono esters with allenylpinacolborate in aqueous media (Scheme 49). 102 Divergent reac-tivity was displayed under either copper(II)-or bismuth(III)-catalyzed conditions. The use of a catalytic quantity of copper(II) hydroxide resulted in the predominant formation of the propargylated product 179.…”