Reactions of 1-trifluoromethyl-propyne 1-iminium salts with nitroanilines: synthesis of 4-CF3-nitroquinolines and 1,2,3-trisubstituted-5-CF3-pyrroles

A variety of 4-CF3-quinolines bearing an aryl (or cyclopropyl, tert-butyl, trimethylsilyl) group at C-2 and a nitro group at ring position 6, 7 or 8 have been prepared in good to high yields from 3-substituted 1-CF3-prop-2-yne 1-iminium triflate salts and o-, m- or p-nitroaniline. These reactions include an aza-Michael reaction at room temperature followed by an intramolecular electrophilic aromatic substitution step, which requires additional thermal activation in most cases. In contrast, the conjugate addition of 2,4-dinitroanilines at the acetylenic iminium ions proceeds much more slowly and some of the adducts can be converted thermally into 2-(2,4-dinitrophenyl)-5-CF3-pyrroles. Analogously, 2-(4-pyridyl)-5-CF3-pyrroles were obtained from 3-aryl-1-CF3-propyne iminium salts and 4-aminopyridinium triflate. A novel variation of the Truce-Smiles rearrangement is probably involved in the formation of these pyrroles.

Enantioselective Radical Functionalization of Imines and Iminium Intermediates via Visible Light Photoredox Catalysis

Visible light photoredox catalysis has recently emerged as a powerful tool for the development of new and valuable chemical transformations under mild conditions. Visible-light promoted enantioselective radical transformations of imines and iminium intermediates provide new opportunities for the asymmetric synthesis of amines and asymmetric β-functionalization of unsaturated carbonyl compounds. In this review, the advance in the catalytic asymmetric radical functionalization of imines, as well as iminium intermediates, are summarized. 1 Introduction 2 The enantioselective radical functionalization of imines 2.1 Asymmetric reduction 2.2 Asymmetric cyclization 2.3 Asymmetric addition 2.4 Asymmetric radical coupling 3 The enantioselective radical functionalization of iminium ions 3.1 Asymmetric radical alkylation 3.2 Asymmetric radical acylation 4 Conclusion

Stereoselective synergystic organo photoredox catalysis with enamines and iminiums

Graphical AbstractApplication of small chiral organic molecules in catalysis has been dominated by formation of chiral enamines or iminium ions. Nucleophiles – electrophiles reactivity has been exploited in many papers. Now, the possibility to combine organocatalysis with photochemistry open new “exciting” possibilities and opportunities, in reactions that are mediated by radicals.

Experimental and Computational Studies Unraveling the Peculiarity of Enolizable Oxoesters in the Organocatalyzed Mannich-Type Addition to Cyclic N-Acyl Iminium Ions

γ− and δ-Oxoesters are easily available starting materials that have been sparingly used in some organocatalyzed reactions proceeding with a high enantioselectivity. In our experimentation we found that the use of these compounds as the enolizable (nucleophilic) component in organocatalyzed Mannich-type reactions using in situ-generated cyclic N-acyl iminium ions gave low diastereoselectivity and low to moderate values of enantioselectivity. This significant drop of facial selectivity with respect to simple aliphatic aldehydes has been rationalized by means of density functional theory (DFT) calculations.

Synthetic Studies Towards Spirocyclic Imine Marine Toxins Using N-Acyl Iminium Ions as Dienophiles in Diels–Alder Reactions

Cyclic imine marine toxins have attracted considerable attention from the synthetic community in the past two decades due to their unique chemical structures and clinically relevant biological activities. This review presents recent efforts of our group in the development of various strategies to efficiently construct the common spirocyclic imine fragments of the cyclic imine toxins. In particular, the use of α,β-unsaturated N-acyl iminium ion dienophiles in Diels–Alder reactions are highlighted, whereby direct access to spirocyclic imine motifs was obtained and important mechanistic details were discovered. Alternative approaches to spirocyclic imine systems involving hydroamination of amino alkynes are also summarized. One such approach led to serendipitous access to N-vinyl amide products, while our most recently ­reported approach involving an intermolecular Diels–Alder/cross-­coupling sequence using novel 2-bromo-1,3-butadienes to access 5,6-spirocyclic imines is also discussed. Additionally, the development of a novel method to construct another challenging motif present in the portimines is also introduced.1 Introduction2 Strategies towards the Spirocyclic Imine Fragment of Cyclic Imine Toxins2.1 Diels–Alder Cycloadditions of α,β-Unsaturated N-Acyl Iminium Dienophiles2.2 Early Studies Using in situ-Generated Iminium Ion Dienophiles2.3 Use of More Stable Iminium Ion Dienophiles for Diels–Alder Reactions2.4 Other Notable Strategies towards Spirocyclic Imines2.5 Recent Efforts towards the 5,6-Spirocyclic Imine Marine Toxin Portimine A2.6 Construction of Another Challenging Motif of Portimine A3 Conclusion and Future Perspectives