Asymmetric allylation of aryl aldehydes: studies on the scope and mechanism of the palladium catalysed diethylzinc mediated umpolung using phosphoramidite ligands

Phosphoramidite: privilegierte Liganden in der asymmetrischen Katalyse

“…[356][357][358][359][360] Hierbei wurden die Aldehyde 234 mit Cyclohexylacetat 233 und Palladiumkatalysatoren auf der Basis von Phosphoramidit-Liganden (Schema 74) umgesetzt. [361] Die vermutlich intermediär aus dem Allylpalladiumkomplex entstehende Allylzinkverbindung wurde mit verschiedenen Aldehyden 234 abgefangen, wobei die syn-Homoallylalkohole 235 mit Ausbeuten bis 82 %, ee-Werten bis 81 % und in allen Fällen hervorragenden Diastereoselektivitäten (> 20:1) gebildet wurden. Die bisher höchsten Selektivitäten lieferte der Phosphoramidit-Ligand L2a (siehe Abbildung 4).…”

Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes, Aryldiazonium Salts, and Aldehydes

“…Zuschriften hydes,t he installation of substituents or heteroatoms on the aryl group was allowed, thus resulting in high yields and excellent selectivities (entries [1][2][3][4]. Notably,t he successful multicomponent reaction of unsaturated aldehydes proceeded with excellent results (entries 5a nd 6).…”

“…[4] Recently,Krische and co-workers established ah ighly atom-economic C À H crotylation of primary alcohols by hydrohydroxyalkylation of butadiene enabled by ac ombined ruthenium(II) and chiral phosphoric acid catalysis (Scheme 1b). [5] Very recently,w e accomplished ahighly stereoselective allylation of aldehydes with terminal alkenes based on allylic CÀHactivation enabled by combined palladium and Brønsted acid catalysis,a lbeit with moderate enantioselectivity.…”

“…[1] As such, the creation of new synthetic methods to access these molecules has long and continuously received widespread attention. [2][3][4] Traditionally, the most reliable methods rely on the stereoselective addition of allylic metal reagents to carbonyl groups,asdemonstrated by many well-known and widely applicable reactions.…”

Reactions of Aldehydes and Ketones and their Derivatives

“…171 BINOL-derived phosphoramidites are versatile ligands in palladium-catalysed umpolung allylation of aryl aldehydes mediated by diethylzinc. 172 The possible roles of ee allyl-zinc and -palladium species in the mechanism are discussed in detail.…”