Modular P-Chirogenic Phosphine-Sulfide Ligands: Clear Evidence for Both Electronic Effect and P-Chirality Driving Enantioselectivity in Palladium-Catalyzed Allylations

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• 作者：J茅r么me Bayardon ; Mil猫ne Maronnat ; Adam Langlois ; Yoann Rousselin ; Pierre D. Harvey ; Sylvain Jug茅
• 刊名：Organometallics
• 出版年：2015
• 出版时间：September 14, 2015
• 年：2015
• 卷：34
• 期：17
• 页码：4340-4358
• 全文大小：680K
• ISSN：1520-6041

文摘

Using the ephedrine methodology, modular stereoselective syntheses of a new class of P-chirogenic phosphines bearing a sulfur-chelating arm (P*,S-hybrid ligand) are described. A first series of syntheses based on a Fries-like rearrangement of P-chirogenic phosphinite-boranes, which are prepared from 2-bromobenzyl or 2-bromophenethyl alcohol and are mediated by metal鈥揾alide exchange, have been performed. This rearrangement affords phosphine-boranes stereospecifically with an o-hydroxyalkylphenyl substituent. The latter residue is subsequently converted into a sulfur-containing group. In a second series, the stereoselective syntheses were achieved according to a new strategy involving a reaction of a thiophenyllithium reagent with a P-chirogenic phosphinite. The X-ray structures of the P*,S ligands and their palladium complexes allow us to address the absolute configuration at both the phosphorus and sulfur centers. The P*,S ligands were used in palladium-catalyzed allylic alkylations, as tests, affording asymmetric inductions up to 96% ee. Computer modeling corroborates the regio- and enantioselectivity of the Pd-catalyzed allylations and the low influence of the substituent carried by the sulfur moiety, particularly when the chelate forms a six-membered ring with the metal.