Tf2O-Mediated Cyclization of α-Acyl-β-(2-aminopyridinyl)acrylamides: Access to N-Substituted 4H-Pyrido[1,2-a]pyrimidin-4-imines

Triflic Acid-Promoted 1,2-Amino Migration Reactions in α-Arylaminoacrylamides: Access to Substituted β-Aminoamides

A straightforward synthesis of substituted β-aminoamides from α-arylamino-β-hydroxyacrylamides, α-arylamino-β-oxoamides, or their tautomeric mixture has been described. The (E)-enol triflate intermediates are readily generated in situ from these substrates in the presence of triflic anhydride (Tf2O) and triethylamine (Et3N) in a chemoselective manner and undergo triflic acid (TfOH)-promoted cyclization and ring-opening reactions with alcohols to deliver the desired products. The one-pot two-step synthetic protocol features the use of readily available starting materials, mild reaction conditions, high chemoselectivity, operational simplicity, and a wide range of synthetic potential of the products.

Triflic Anhydride (Tf2O)-Activated Transformations of Amides, Sulfoxides and Phosphorus Oxides via Nucleophilic Trapping

Trifluoromethanesulfonic anhydride (Tf2O) is utilized as a strong electrophilic activator in a wide range of applications in synthetic organic chemistry, leading to the transient generation of a triflate intermediate. This versatile triflate intermediate undergoes nucleophilic trapping with diverse nucleophiles to yield novel compounds. In this review, we describe the features and applications of triflic anhydride in organic synthesis reported in the past decade, especially in amide, sulfoxide, and phosphorus oxide chemistry through electrophilic activation. A plausible mechanistic pathway for each important reaction is also discussed.

1 Introduction

2 Amide Chemistry

2.1 Carbon Nucleophiles

2.2 Hydrogen Nucleophiles

2.3 Nitrogen Nucleophiles

2.4 Oxygen and Sulfur Nucleophiles

2.5 hosphorus Nucleophiles

2.6 A Vilsmeier-Type Reagent

2.7 Umpolung Reactivity in Amides

3 Sulfoxide Chemistry

3.1 Oxygen Nucleophiles

3.2 Carbon Nucleophiles

3.3 Nitrogen Nucleophiles

3.4 Thionium Reagents

4 Phosphorus Chemistry

4.1 Hendrickson’s Reagent

4.2 Diaryl Phosphine Oxides

4.3 Phosphonates, Phosphates and Phosphinates

5 Conclusion and Outlook