Hydroxylamines as Oxygen Atom Nucleophiles in Transition-Metal-Catalyzed Allylic Substitution

Abstract

[reaction: see text] The viability of hydroxylamines as nucleophiles in transition-metal-catalyzed allylic substitutions was examined. We have found that the oxygen atom of hydroxylamines having an N-electron-withdrawing substituent (also known as hydroxamic acids) acts as a reactive nucleophile. The palladium-catalyzed O-allylic substitution of hydroxylamines with allylic carbonate afforded the linear hydroxylamines. The selective formation of the branched hydroxylamines was observed in iridium-catalyzed reaction. Regio- and enantioselective allylic substitution of the unsymmetrical phosphates with hydroxylamines was studied by using the iridium complex of chiral pybox ligand. The aqueous-medium reaction with hydroxylamines proceeded smoothly in the presence of Ba(OH)(2).H(2)O to give the branched products with good enantioselectivities.

Metal‐Catalyzed Enantioselective Allylation in Asymmetric Synthesis

“…[272] Singh and Han very recently demonstrated that allylamine 282 can be prepared (70-92 % yield, 92 to > 99 % ee) by the regio-and enantioselective decarboxylative allylic amidation reaction of allylbenzyl imidodicarbonates 281 (Scheme 91). [273] 4.1.1.3.…”

Regio- and Enantioselective Allylic Substitution with Less Active N- or O-Nucleophiles Catalyzed by Iridium-Complex of Bis(oxazolinyl)pyridine

“…Recently, we reported that the iridium-complex of pybox catalyzed allylic substitution of unsymmetrical substrates to form branched products with good enantioselectivities. 13,14,17,19) Prior to exploring the enantioselective reaction, we first investigated the viability of hydroxylamine 4A having N-benzoyl and O-benzyl groups (Chart 1). Although the reaction of 4A with carbonate 7 was less effective in the absence of a base, the reaction of 4A with acetate 8 proceeded smoothly by employing Et 2 Zn as a base to give the branched product 9Aa in 60% yield without formation of the linear product.…”

“…1). 17,18) As a part of our program directed toward searching the synthetically useful heteroatom nucleophiles, we describe in detail the study of hydroxylamines 4 as nitrogen nucleophiles in the regio-and enantioselective iridium-catalyzed allylic substitutions. 19) In this study, we also expected that comparison with alkylamines, p-anisidine, and 4-methoxyphenol would lead to informative suggestions regarding the asymmetric reaction using the iridium complex of pybox (bis(oxazolinyl)pyridine) ligand.…”

Metallkatalysierte enantioselektive Allylierungen in der asymmetrischen Synthese

“…[260] 4. Iridiumkatalysierte enantioselektive Allylierungen [261] Iridiumkomplexe mit chiralen Liganden wie dem Phosphan-Oxazolin L196, [262] (S)-1,1'-Binaphthyl-2,2'-diylphenylphosphit L197, [263] oder den Phosphoramiditen L198 [264] [272] Han et al haben kürzlich die Synthese der Allylamine 282 (70-92 % Ausbeute, 92 bis über 99 % ee) durch regio-und enantioselektive decarboxylierende allylische Amidierung der Allylbenzylimidodicarbonate 281 beschrieben (Schema 91). [273] [274][275] Die Allylierung des Oxims 284 mit 272 a verlief glatt und ergab das verzweigte (E)-Benzaldehyd-O-1-phenyl-2-propenyloxim (285) mit hoher Enantioselektivität (Schema 93).…”

“…[273] [274][275] Die Allylierung des Oxims 284 mit 272 a verlief glatt und ergab das verzweigte (E)-Benzaldehyd-O-1-phenyl-2-propenyloxim (285) mit hoher Enantioselektivität (Schema 93). [272] Carreira et al entwickelten eine effiziente Synthese der chiralen Allylalkohole 287: Durch regioselektive iridiumkatalysierte allylische Veretherung in Gegenwart des Liganden (S,S, a S)-L198 wurden aus einer Reihe aryl-und alkylsubstituierter Allylphosphate 272 mit dem Kaliumsilanolat 286 die entsprechenden Allylsilylether erhalten, die zu den optisch aktiven Allylalkoholen 287 hydrolysiert wurden (92-99 % ee, Schema 94). [276] …”