Enantioselective isothiourea-catalysed trans-dihydropyridinone synthesis using saccharin-derived ketimines: scope and limitations

Enantioselective Construction of Tertiary α-Alkyl Fluoride via BTM-Catalyzed Fluorination of α-Alkynyl-Substituted Acetic Acids

The isothiourea-catalyzed enantioselective construction of tertiary α-fluoro stereogenic centers has been demonstrated by using branched alkynyl-substituted acetic acids as starting materials, providing a broad range of optically active tertiary α-alkyl fluorides in high enantioselectivity (up to 97% ee). Furthermore, this methodology was proven to be scaled up to a Gram scale without loss of enantioselectivity.

Catalytic enantioselective synthesis of 1,4-dihydropyridines via the addition of C(1)-ammonium enolates to pyridinium salts

The regio- and stereoselective addition of C(1)-ammonium enolates - generated in situ from aryl esters and the isothiourea catalyst (R)-BTM - to pyridinium salts bearing an electron withdrawing substituent in the 3-position allows the synthesis of a range of enantioenriched 1,4-dihydropyridines. This represents the first organocatalytic approach to pyridine dearomatisation using pronucleophiles at the carboxylic acid oxidation level. Optimisation studies revealed a significant solvent dependency upon product enantioselectivity, with only toluene providing significant asymmetric induction. Using DABCO as a base also proved beneficial for product enantioselectivity, while investigations into the nature of the counterion showed that co-ordinating bromide or chloride substrates led to higher product er than the corresponding tetrafluoroborate or hexafluorophosphate. The scope and limitations of this process are developed, with enantioselective addition to 3-cyano- or 3-sulfonylpyridinium salts giving the corresponding 1,4-dihydropyridines (15 examples, up to 95 : 5 dr and 98 : 2 er).

[2.2]Paracyclophane-Based Isothiourea-Catalyzed Highly Enantioselective α-Fluorination of Carboxylic Acids

Planar chiral [2.2]paracyclophane-based isothiourea catalysts have been prepared over a few simple steps in high yields. In the presence of these catalysts, highly efficient catalytic enantioselective fluorination of carboxylic acids has been accomplished, providing a broad range of optically active α-fluoroesters in high yield and excellent enantioselectivity.

Generation and Reactivity of C(1)-Ammonium Enolates by Using Isothiourea Catalysis

C(1)-Ammonium enolates are powerful, catalytically generated synthetic intermediates applied in the enantioselective α-functionalisation of carboxylic acid derivatives. This minireview describes the recent developments in the generation and application of C(1)-ammonium enolates from various precursors (carboxylic acids, anhydrides, acyl imidazoles, aryl esters, α-diazoketones, alkyl halides) using isothiourea Lewis base organocatalysts. Their synthetic utility in intra- and intermolecular enantioselective C-C and C-X bond forming processes on reaction with various electrophiles will be showcased utilising two distinct catalyst turnover approaches.

Tandem sequential catalytic enantioselective synthesis of highly-functionalised tetrahydroindolizine derivatives

An isothiourea-catalysed enantioselective synthesis of novel tetrahydroindolizine derivatives is reported through a one-pot tandem sequential process. The application of 2-(pyrrol-1-yl)acetic acid in combination with either a trifluoromethyl enone or an α-keto-β,γ-unsaturated ester in an enantioselective Michael addition–lactonisation process, followed by in situ ring-opening and cyclisation, led to a range of 24 tetrahydroindolizine derivatives containing three stereocentres in up to >95 : 5 dr and >99 : 1 er.

The isothiourea-catalysed enantioselective synthesis of tetrahydroindolizine derivatives containing three stereocentres is reported through a one-pot tandem sequential process.

An asymmetric Mannich reaction of α-diazocarbonyl compounds and N-sulfonyl cyclic ketimines catalyzed by complexes generated from chiral and achiral phosphines with gold(i)

An unprecedented Lewis acidic gold(i)-complex generated from chiral and achiral phosphines has been developed for the Mannich reaction of α-diazocarbonyl compounds and N-sulfonyl cyclic ketimines. A series of chiral β-amino-α-diazoesters bearing a quaternary stereocenter were obtained in high yields with good enantioselectivities. In addition, the products could be converted to promising bioactive spirosuccinimide. Furthermore, operando IR, NMR and control experiments were carried out to gain insight into the mechanism.

Asymmetric Synthesis of cis-3,4-Dihydrocoumarins via [4 + 2] Cycloadditions Catalyzed by Amidine Derivatives

A highly efficient chiral amidine derivative-catalyzed tandem Michael addition/lactonization of carboxylic acids and o-quinone methides (o-QMs) has been developed that enables the asymmetric synthesis of cis-3,4-dihydrocoumarins bearing contiguous tertiary stereogenic centers in high yields with excellent stereoselectivities.