Electrophilic activation of aminocarboxylic acid by phosphate ester promotes Friedel-Crafts acylation by overcoming charge-charge repulsion

Palladium-Catalyzed Decarbonylative Sonogashira Alkynylation of Carboxylic-Phosphoric Anhydrides

We report the first palladium-catalyzed decarbonylative alkynylation of carboxylic-phosphoric anhydrides via highly selective C(O)-O bond cleavage. Carboxylic-phosphoric anhydrides are highly active carboxylic acid derivatives, which are generated through activating carboxylic acids using phosphates by esterification or direct dehydrogenative coupling with phosphites. Highly valuable internal alkynes have been generated by the present method, and the efficiency of this approach has been demonstrated through a wide substrate scope and excellent functional group tolerance.

窒素原子を含む結合活性化学種の発見

In this review, the authors review and explain their research on "Discovery of Bonding Active Species Containing Nitrogen Atoms" from the past to the present. The authors are interested in new chemical phenomena, especially in the activation of chemical bonds containing nitrogen atoms, and have conducted research to discover chemical bonds with new properties. The activated chemical bonds containing nitrogen atoms are the following (Fig. 1). (1) Rotationally activated C-N bonds by pyramidalization of amide nitrogen atoms (2) N-N bond cleavage ability with reduced bond strength by pyramidalization of nitrosamine nitrogen atoms (3) Transient hetero atom-N bond formation by neighboring group participation of a halogen electron to the nitrogen cation. (4) A unique carbon cation reaction involving nitrogen atoms, especially nitro groups (C-NO₂ bond) and ammonium ions (C-NH₃⁺ bond). These purely basic chemistry discoveries unexpectedly led to the creation of functional materials, especially biologically active molecules. We will explain how new chemical bonds led to the creation of new functions.

Friedel-Crafts Acylation of Aminocarboxylic Acids in Strong Brønsted Acid Promoted by Lewis Base P4O10

The amino group in aminocarboxylic acids is sufficiently basic to be protonated in strong acids, and consequently, ionization of the carboxylic acid to an acylium ion is blocked due to charge-charge repulsion. Thus, acylation of aromatic compounds is significantly retarded in Friedel-Craft type reactions. We found that Friedel-Crafts acylation with aminocarboxylic acids can proceed smoothly even in a strong Brønsted acid (triflic acid, TfOH) if the Lewis base P₄O₁₀ is added. Here we describe the Friedel-Crafts acylation reactions of anthranilic acid and α- to δ-aminocarboxylic acids with benzene derivatives in the presence of P₄O₁₀. Non-amino-containing carboxylic acids as well as N-containing heteroaromatic carboxylic acids are available, and α-amino acids can be directly utilized without any protective group. Most substrates afford acylation products in high yields, although some epimerization/racemization may occur. Density functional theory (DFT) calculations suggested that P₄O₁₀ neutralizes the protonated amine, converting the N-H covalent bond to a N-hydrogen bond and allowing the carboxylic acid OH functionality to serve as a good leaving group.

Friedel-Crafts-Type Acylation and Amidation Reactions in Strong Brønsted Acid: Taming Superelectrophiles

In this review, we discuss Friedel-Crafts-type aromatic amidation and acylation reactions, not exhaustively, but mainly based on our research results. The electrophilic species involved are isocyanate cation and acylium cation, respectively, and both have a common ⁺C=O structure, which can be generated from carboxylic acid functionalities in a strong Brønsted acid. Carbamates substituted with methyl salicylate can be easily ionized to the isocyanate cation upon (di)protonation of the salicylate. Carboxylic acids can be used directly as a source of acylium cations. However, aminocarboxylic acids are inert in acidic media because two positively charged sites, ammonium and acylium cation, will be generated, resulting in energetically unfavorable charge-charge repulsion. Nevertheless, the aromatic acylation of aminocarboxylic acids can be achieved by using tailored phosphoric acid esters as Lewis bases to abrogate the charge-charge repulsion. Both examples tame the superelectrophilic character.

Superelectrophiles: Recent Advances

Superelectrophiles are reactive species that often carry multiple positive charges. They have been useful in numerous synthetic methods and they often exhibit highly unusual reactivities. Recent advances in superelectrophile chemistry are discussed in this review.

Facile synthesis of 2,3-benzodiazepines using one-pot two-step phosphate-assisted acylation–hydrazine cyclization reactions

We present a one-pot two-step methodology, in which an unprotected amino is tolerated, for rapidly synthesizing 2,3-benzodiazepines via phosphate-assisted acylation reaction and hydrazine cyclization reaction.