Electrophilic Chemistry of Biologically Important α-Ketoacids

Superelectrophiles in Synthesis: Preparation of Aromatic Imides

Aromatic carboxylic acids are found to undergo reactions with isocyanates, wherein triflic acid promotes the formation of aromatic imide products in fair to good yields. It is proposed that the carboxylic acid group directs the isocyanate electrophile to the ortho-position. This is thought to occur by the formation of a temporary carbamic acid anhydride group, which cleaves upon ortho-functionalization. A series of imide products are synthesized, and the synthesis of a potential selective inhibitor of tyrosyl DNA phosphodiesterase II is performed.

SUPERACID-PROMOTED HYDROXYALKYLATION OF 1,2-INDANDIONES

1,2-Indandione reacts efficiently with arenes to give 2,2-diaryl-1-indanones by the hydroxyalkylation reaction. The Brønsted superacid CF₃SO₃H (triflic acid) is an effective catalyst for these condensation reactions. The requisite 1,2-indandiones were prepared from the 1-indanones.

Superacid-Catalyzed Reactions of Cinnamic Acids and the Role of Superelectrophiles1

The chemistry of cinnamic acids and related compounds has been studied. In superacid-catalyzed reactions with arenes, two competing reaction mechanisms are proposed. Both mechanisms involve the formation of dicationic intermediates (superelectrophiles), and the reactions can lead to either chalcone-type products or indanone products. The direct observation of a dicationic species (by low-temperature (13)C NMR) is reported. We provide clear evidence that protonated carboxylic acid groups (or the corresponding acyl cation) can enhance the reactivity of an adjacent electrophilic center. Triflic acid is also found to be an effective acid catalyst for the direct synthesis of some electron-deficient chalcones and heterocyclic chalcones from cinnnamic acids.

Carbopalladation of nitriles: synthesis of benzocyclic ketones and cyclopentenones via Pd-catalyzed cyclization of omega-(2-iodoaryl)alkanenitriles and related compounds

An efficient procedure for the synthesis of 2,2-disubstituted benzocyclic ketones by intramolecular carbopalladation of nitriles has been developed. The cyclization of substituted 3-(2-iodoaryl)propanenitriles affords indanones in high yields. The reaction is compatible with a wide variety of functional groups. This methodology has been extended to the synthesis of tetralones and cyclopentenones.

Electrophilic activation of acetyl-substituted heteroaromatic compounds

The chemistry of acetyl-substituted pyridines, thiazoles, quinoline, isoquinolines, and pyrazine (1-9 and 28) has been studied. These heteroarenes (1-8) condense with benzene in good yields (74-96%) in the Bronsted superacid, CF(3)SO(3)H (triflic acid). In these acid-catalyzed hydroxyalkylation reactions, compounds 1-8 are significantly more reactive than acetophenone. It is proposed that compounds 1-8 readily form dicationic electrophiles in triflic acid.