Effect of amine structure and reaction additives on enantioselective deprotonations mediated by homochiral magnesium amide bases

Magnesium Catalysis in Asymmetric Synthesis

“…A typical reaction that can be used to compare different in-situ-generated magnesium complexes prepared by bi-H-bond or mono-H-bond methods is the enantioselective deprotonation of ketones to generate chiral enolate silyl ethers developed by Kerr, Henderson, and coworkers. [85][86][87][88][89] As summarized in Scheme 41, the enantioselective deprotonation of cyclohexanone can be achieved by different magnesium catalysts with either bi-H-bond or mono-H-bond ligands or a combination of the two ligand methods. The addition of the second ligand in the combinational strategies using magnesium catalysts resulted in very different catalytic activities.…”

“…Although the utilization of a phenol as the second ligand did not improve the enantioselective deprotonation reaction, this proposed strategy implies that the addition of another Brønsted acid to form a combinational magnesium catalyst would dramatically change the properties of the Mg(II) complex, and this could be an alternative strategy for tuning the catalyst's activity. [85][86][87][88][89] A classic example of employing a second covalent ligand in a magnesium catalyst to achieve high enantioselectivity was reported by Trost and coworkers. 90,91 Using their ProPhenol ligand, a magnesium-catalyzed direct asymmetric Aldol addition of ethyl diazoacetate to aldehydes was achieved.…”

Synthesis of Polymer‐Supported Chiral Lithium Amide Bases and Application in Asymmetric Deprotonation of Prochiral Cyclic Ketones.

“…12, 13 Henderson systematically studied magnesium amide base-mediated enantioselective deprotonation processes. 14,15 Despite the increasing use of polymeric chiral reagents in organic synthesis, the number of papers dealing with asymmetric deprotonation using polymer-supported CLAB's is still limited. 16,17,18 The polymer-supported CLAB's share several common advantages as other supported reagents utilized in solid phase organic synthesis (SPOS), such as easy separation of the products, and simple recycling of supported CLAB's by filtration which is important for precious demanding ligands.…”

Synthesis of polymer-supported chiral lithium amide bases and application in asymmetric deprotonation of prochiral cyclic ketones

“…12, 13 Henderson systematically studied magnesium amide base-mediated enantioselective deprotonation processes. 14,15 Despite the increasing use of polymeric chiral reagents in organic synthesis, the number of papers dealing with asymmetric deprotonation using polymer-supported CLAB's is still limited. [16][17][18] The polymer-supported CLAB's share several common advantages as other supported reagents utilized in solid phase organic synthesis (SPOS), such as easy separation of the products, and simple recycling of supported CLAB's by filtration, which is important for precious demanding ligands.…”