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This short review highlights select examples of enantioselective Lewis base promoted reactions that use tertiary amine (cinchona alkaloids, isothioureas, and DMAP/PPY derivatives) or NHC catalysts and employ aryloxide-promoted catalyst turnover from an acyl ammonium or azolium intermediate. This review focuses on the range of strategies that have been developed within this area, and discusses their evolution and context. 1 Introduction 2 Phenols as Additives To Promote Catalyst Turnover 2.1 NHC Catalysis with a-Functionalised Aldehydes and Phenols 2.2 Enantioselective Fluorination with Aryloxide-Promoted Catalyst Turnover 3 In Situ Catalytic Generation Of Aryloxide 3.1 Aryloxide-Promoted Turnover Generated from an Electrophilic Polyhalogenated Quinone: Overview 3.2 Aryloxide-Promoted Catalyst Turnover Generated from an a-Aryloxyaldehyde or Aryl Ester Starting Material: Overview 4 Summary and Outlook. [ABSTRACT FROM AUTHOR]

The scope of dihydropyranone and dihydropyridinone products accessible by isothiourea-catalyzed processes has been expanded and explored through the use of 2- N-tosyliminoacrylates and 2-aroylacrylates in a Michael addition-lactonization/lactamization cascade reaction. Notably, to ensure reproducibility it is essential to use homoanhydrides as ammonium enolate precursors with 2-aroyl acrylates, while carboxylic acids can be used with 2- N-tosyliminoacrylates, delivering a range of 3,5,6-substituted dihydropyranones and dihydropyridinones with high enantioselectivity (typically >90 % ee). The derivatization of the heterocyclic core of a 3,5,6-substituted dihydropyranone through hydrogenation is also reported. [ABSTRACT FROM AUTHOR]

Anisothiourea-catalyzed Michael addition–lactamizationfollowed by the sulfide oxidation–elimination/N- to O-sulfonyl transfer sequence for the formationof 2,3,5- and 2,3-substituted pyridine 6-tosylates from (phenylthio)aceticacids and α,β-unsaturated ketimines is described. Incorporationof the valuable 2-sulfonate group allows derivatization to a rangeof di-, tri-, and tetrasubstituted pyridines. [ABSTRACT FROM AUTHOR]

The scope of dihydropyranone and dihydropyridinone products accessible by isothiourea-catalyzed processes has been expanded and explored through the use of 2-N-tosyliminoacrylates and 2-aroylacrylates in a Michael addition-lactonization/lactamization cascade reaction. Notably, to ensure reproducibility it is essential to use homoanhydrides as ammonium enolate precursors with 2-aroyl acrylates, while carboxylic acids can be used with 2-N-tosyliminoacrylates, delivering a range of 3,5,6-substituted dihydropyranones and dihydropyridinones with high enantioselectivity (typically >90 % ee). The derivatization of the heterocyclic core of a 3,5,6-substituted dihydropyranone through hydrogenation is also reported., (© 2015 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

Isothiourea HBTM-2.1 catalyses the Michael addition-lactonisation of 2-aryl and 2-alkenylacetic acids and α,β-unsaturated trichloromethyl ketones. Ring-opening of the resulting dihydropyranones and subsequent alcoholysis of the CCl3 ketone with an excess of methanol gives a range of diesters in high diastereo- and enantioselectivity (up to 95 : 5 dr and >99% ee). Sequential addition of two different nucleophiles to a dihydropyranone gives the corresponding differentially substituted diacid derivative.

The partial reduction of electron deficient pyrroles is an extremely versatile method that allows us to prepare substituted pyrrolidines and pyrrolizidines with trans-diol stereochemistry on the five membered ring.