Metal Ion Catalysis in Nucleophilic Substitution Reactions Promoted by Complexes of Polyether Ligands with Alkali Metal Salts

Arylsulfonate-Based Nucleophile Assisting Leaving Groups

“…The crude oil (1.5 g, 6.2 mmol) was then dissolved in excess methoxyethanol (2.5 g, 32 mmol) and heated to 60 °C for 30 h. The reaction mixture was purified by flash chromatography by eluting with a hexane/acetone (85:15 v/v) to yield 1b as white solid: (1. 6 Representative Procedure: Preparation of 3-Phenyl-propyl 2-(2-Oxobutylcarboxy)-1-benzosulfonate (2b). To a dichloromethane solution (10 mL) of 1b (0.536 g, 1.92 mmol) was added DMAP (0.25 g, 2.08 mmol) under argon.…”

“…The chelated metal cation would also be expected to stabilize the developing negative charge on the oxygens of the sulfonate leaving group in the transition state. 6 In addition, by attaching an ion-selective moiety to the leaving group, the electrophilic substrate should be more reactive toward nucleophiles containing a specific metal countercation potentially leading to the development of salt-specific leaving groups. 7 In this report, we describe the unique reactivity of arylsulfonate-based nucleophile assisting leaving groups (NALG) that contain either acyclic or macrocyclic ether units attached to the aryl ring ortho to the sulfonate.…”

Polyoxaethylene polypodands - powerful reduction catalysts in solid-liquid and liquid-liquid phase transfer systems

“…This is a result of the charge density in the complex of podand ligands with Li + being higher than those in the complexes with other alkali metals. [18][19][20] As the reaction of benzaldehyde reduction with LiBH 4 under PTC conditions (with the use of the ligands described here as catalysts) runs in the presence of Lewis acids (AlCl 3 and ZrCl 4 were checked as an activators), it seems that the first explanation of the lithium borohydride/podand systems inactivity as reductors is correct ( Table 2). The addition of such an acid to the inactive system induces the coordination of AlCl 3 (or ZrCl 4 ) to the benzaldehyde oxygen atom (C¼OÁÁÁMCl x ) and activates the carbonyl group, which permits its reduction.…”

Recent Advances in Heterolytic Nucleofugal Leaving Groups

“…The increased reaction rate of LiBr relative to NaBr and KBr for all NALGs 144 appear to parallel earlier intermolecular studies involving alkylmesylate reactions with various metal iodide salts. 108 The presence of ethylene oxide units increase the relative rate of LiBr versus NaBr additions to 50 fold for 144b (n = 1) and 160 fold 144c (n = 2). The trend seems to level off with additional ethylene oxide units.…”