Phase-transfer catalysis has been recognized as a powerful method for establishing practical protocols for organic synthesis, because it offers several advantages, such as operational simplicity, mild reaction conditions, suitability for large-scale synthesis, and the environmentally benign nature of the reaction system. Since the pioneering studies on highly enantioselective alkylations promoted by chiral phase-transfer catalysts, this research field has served as an attractive area for the pursuit of "green" sustainable chemistry. A wide variety of asymmetric transformations catalyzed by chiral onium salts and crown ethers have been developed for the synthesis of valuable organic compounds in the past several decades, especially in recent years.

A practical and efficient method for the synthesis of cyclic carbonates from epoxides and CO2 under mild reaction conditions was achieved via the use of a potassium iodide (KI)–tetraethylene glycol complex as a readily available and economical catalyst. The effects of glycols and alkali metal salts were investigated in the present work to clarify the importance of both KI and tetraethylene glycol. Scalability and reusability of this catalytic system were also demonstrated.

A protocol for the dehydrative nucleophilic substitution of benzyl alcohols with a variety of carbon- and heteroatom-centered nucleophiles using dodecylbenzenesulfonic acid (DBSA) as a surfactant-type Brønsted acid catalyst in water has been developed. The reaction system can be applied to the stereoselective C-glycosylation of 1-hydroxy sugars in water. [reaction: see text].

Phase-transfer catalysis (PTC) has been recognized as a convenient and highly useful tool in academia and industry because it offers several advantages for practical organic synthesis, such as operational simplicity, mild reaction conditions in aqueous media, environmental benefits, and suitability for large-scale reactions. [1,2] Also the development of efficient methods for the preparation of natural and nonnatural a-alkyl-and a,a-dialkyl-a-amino acids, especially in their enantiomerically pure forms by asymmetric PTC, has become very important because of their high synthetic utility. [3, 4] Accordingly, several phase-transfer catalysts have been developed that lead to products with excellent enantioselectivities in high yields.[4] However, despite numerous studies, truly efficient catalytic systems with high enantioselection at very low catalyst loading (e.g., < 0.1 mol %) are still rare in asymmetric carbon-carbon bond formation, and major progress in terms of catalyst loading is still desirable for practical asymmetric synthesis. Since our recently developed, chiral spiro-type (R,R)-or (S,S)-3,4,5-trifluorophenyl-NAS bromide 1 shows exceedingly high enantioselectivity in asymmetric alkylation of a-amino acid derivatives, [4d,e,m] our next target was the design of a very active catalyst. Considering the highly lipophilic nature of 1 and the generation of a metal enolate in an interfacial layer, [5] such lipophilic 1 (QX) must move to the interfacial layer to induce a facile exchange reaction with a metal enolate (Scheme 1). Based on this assumption, our strategy was to replace the rigid binaphthyl moiety in 1 by flexible straight-chain alkyl groups to furnish a new catalyst of type 2, which substantially accelerates the enolate exchange with 2 because of the increasing polarity of the dialkylammonium moiety. Herein, we report that such a designer chiral quaternary ammonium salt 2 behaves as a very powerful chiral phase-transfer catalyst for the highly practical, enantioselective alkylation of protected-glycine and aalkyl-a-amino acid derivatives.The requisite catalyst (S)-2 can be readily prepared from the commercially available (S)-1,1'-binaphthyl-2,2'-dicarboxylic acid (3) [6] in a six-step sequence as outlined in Scheme 2.[7]Thus, (S)-dicarboxylic acid 3 was transformed with iPrBr, catalytic Bu 4 N·HSO 4 , and KF·2 H 2 O to the corresponding diisopropyl ester 4 in 95 % yield. Treatment of 4 with freshly prepared Mg(TMP) 2 (TMP = 2,2,6,6-tetramethylpiperidide) in THF and subsequent additon of bromine gave rise to (S)-3,3'-dibromo-1,1'-binaphthyl-2,2'-dicarboxylic ester 5 in 91 % yield. Suzuki-Miyaura cross coupling of 5 with 3,4,5-trifluorophenylboronic acid in the presence of catalytic Pd(OAc) 2 , PPh 3 , and K 2 CO 3 in N,N-dimethylformamide (DMF) afforded (S)-3,3'-bis(3,4,5-trifluorophenyl)-1,1'-binaphthyl-2,2'-dicarboxylic ester (6) in 94 % yield. Reduction of 6 with Scheme 1. Proposed mechanism for the generation of chiral ammonium enolate.Scheme 2. a) iPrBr (10 equiv), Bu 4 N·HSO 4 (20 mol %), KF·2 ...