Iridium‐Catalyzed Hydrogenation of β‐Dehydroamino Acid Derivatives Using Monodentate Phosphoramidites

Abstract

The iridium-catalyzed asymmetric hydrogenation of 13 different β-dehydroamino acid derivatives to give optically active β-amino acid esters has been examined. Readily accessible monodentate octahydrobinaphthol-based phosphoramidites were used as chiral ligands. Good to excellent enantioselectivities and yields were obtained for the E isomers, whereas poorer catalyst performance was found for the

Asymmetric NaBH4 1,4‐Reduction of C3‐Disubstituted 2‐Propenoates Catalyzed by a Diamidine Cobalt Complex

“…The present asymmetric catalysis could be also applied to C3-heterosubstituted 1.T hus, C3-CH 3 CONH-substituted ethyl cinnamate 1k and crotonate 1l were quantitatively reduced to the corresponding b-amino acid derivatives with R/S ratios of > 97:3 (entries 13 and 14). [10] The tert-butyldimethylsilyl (TBDMS)-protected enol of a b-keto ester, 1m,w as also reduced with a R/Se rof > 99:1 (entry 15). The esters of tiglic acid and angelica cid were found to be poor substrates.…”

“…The C3-diaryl substituted substrates 1f and 1g werer educed with reasonable enantioselectivity (entries 6a nd 7). The C3-dialkyl-substituted substrates 1h-j were efficiently reduced to give the corresponding saturated products with high enantioselectivities, even with a tert-butyl substituent (entries [8][9][10]. With the diastereomerics ubstrates (Z)-1a and (Z)-1h,t he enantioselectivity was reversed without any negative effect on the er (entries 11 and 12).…”

Iridium‐Catalysed Asymmetric Hydrogenation of Enamides in the Presence of 3,3′‐Substituted H8‐Phosphoramidites

“…[16] Among the highly enantioselective ligands, the pMeO-phenyl-substituted phosphoramidite 1c presented the highest TOF. Notably, the addition of salts like NaClO 4 or NaBF 4 improves the catalytic activity (average TOF estimated from the consumption curve: 22 h…”

“…Soon after, our group used novel 3,3'-disubstituted H8-binaphthophosphoramidites which achieved excellent results in the hydrogenation of a-and b-amino acid precursors. [3,4] In order to demonstrate the relevance of the new catalytic system, further investigations on a more broad scope of functionalised alkenes, such as b-amino acid precursors, were performed. Given our experience in the hydrogenation of aryl-enamides [5] and their attractive potential to form chiral amines, they were selected as subject of our further investigations.…”

Catalytic Synthesis of Optically Active β-Amino Acid Derivatives

“…Also, the combination of Ir(I) and phosphoramidite ligand 39 has been used by Beller and coworkers [88] in 2008 in the hydrogenation of (E)-and (Z)-N-(acylamino)acrylates, affording the product with up to 94% and 67% ee, respectively (Scheme 36 In 2010, Guo et al [89] obtained various -aminomethylacrylates from Baylis-Hillman reaction of aldehydes with methyl acrylate followed by acetylation of the resulting allylic alcohols and S N 2 -type amination of the allylic acetates. These olefinic compounds were then subjected to asymmetric hydrogenation using rhodium (Et-Duphos 40) catalyst to obtain the corresponding 2 -amino acid derivatives with excellent enantioselectivities and exceedingly high reactivities (up to >99.5% ee and substrate (S)/catalyst(C)=10,000), as shown in Scheme 37.…”