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The introduction and development of neutral macrocyclic hosts capable of complexing ions within their pre-organized cavity, has been of utmost importance in supramolecular chemistry. Their ability to form stable organic-soluble metal-macrocycle complexes opened up the way to their application in phase-transfer catalysis (PTC) as a viable alternative to quaternary onium salts. In particular, their conformationally rigid preorganized backbone, accommodating organic substrates in defined orientations, promotes highly efficient stereoselective reactions. This short review summarizes the applications of neutral macrocyclic hosts in stereoselective PTC, highlighting the difference and possible complementarity with quaternary ammonium salts. 1 Introduction 2 Crown Ethers and Related Coronands 2.1 Enantioselective PTC with Chiral Macrocyclic Coronands 2.2 Enantioselective PTC Reactions Catalyzed by Chiral Quaternary Ammonium Salts with Achiral Crown Ether Co-catalysts 3 Cyclic Peptoids 4 Miscellaneous Chiral Macrocyclic Hosts 5 Summary and Outlook. [ABSTRACT FROM AUTHOR]

Nonionic, chiral macrocyclic peptoids are efficient phasetransfer catalysts in the C-4 enantioselective alkylation of 2-[4-(trifluoromethyl) phenyl]-2-oxazoline-4-carboxylic acid esters. Screening of the structural features of cyclic peptoids, namely the ring size, symmetry elements, number of proline residues, and substituents on the side chains, showed that the alternated N-(4-methoxybenzyl)glycine/L-proline cyclohexapeptoid is the optimal catalyst (good yields and up to 75% ee) for the stereocontrolled construction of α-alkylated serine tert-butyl esters. [ABSTRACT FROM AUTHOR]