Chuthamat Duangkamol

An efficient mechanochemical synthesis of amides and dipeptides using 2,4,6-trichloro-1,3,5-triazine and PPh3

A rapid, facile, and efficient mechanochemical synthesis of amides from carboxylic acids has been developed through an in situ acid activation with 2,4,6-trichloro-1,3,5-triazine and a catalytic amount of PPh3. Under room temperature solvent-drop grinding of the reactants in the presence of an inorganic base, a variety of carboxylic acids including aromatic acids, aliphatic acids, and N-protected α-amino acids undergo amidation to afford amides in moderate to excellent yields. The method is also compatible with Fmoc, Cbz, and Boc protecting groups which yields protected optically active dipeptides without detectable racemization.

Significance of reagent addition sequence in the amidation of carboxylic acids mediated by PPh3 and I2

The outcome of the amidation reaction mediated by PPh3–I2 was found to be highly dependent on the addition sequence of the reagents. When triethylamine was subjected to a mixture containing PPh3, I2, and a carboxylic acid, acid anhydride was generated almost instantly, before treatment with an amine, presumably via an attack of carboxylate ion onto the acyl function of an acyloxyphosphonium salt. Nevertheless, when a PPh3–I2 mixture was treated with an amine, then a carboxylic acid, prior to adding the base, amide was rapidly formed in high yield with high chemoselectivity, most likely through an intermediate O,N-pentacoordinate phosphorane species as confirmed by ESI-MS technique.

Facile synthesis of N-acylbenzotriazoles from carboxylic acids mediated by 2,4,6-trichloro-1,3,5-triazine and triethylamine

A facile, efficient, and economic method toward N-acylbenzotriazoles was reported using 2,4,6-trichloro-1,3,5-triazine in combination with triethylamine as a carboxylic acid activator. Through reacting 1H-benzotriazole with the generated triacylated triazine intermediate, a series of N-acylbenzotriazoles could be rapidly prepared in high yields without column chromatography.Graphical abstract

Solvent-free reduction of carboxylic acids to alcohols with NaBH4 promoted by 2,4,6-trichloro-1,3,5-triazine and PPh3 in the presence of K2CO3

A simple, rapid, and eco-friendly method for NaBH4 reduction of carboxylic acids to alcohols under solvent-free conditions was developed using a combination of 2,4,6-trichloro-1,3,5-triazine (TCT) with a catalytic amount of triphenylphosphine as an acid activator. With the 1 : 0.2 : 1.5 : 2 mole ratio of TCT : PPh3 : K2CO3 : NaBH4, carboxylic acids including aromatic acids, aliphatic acids, and N-protected α-amino acids (Fmoc, Z) could readily undergo reduction to give the corresponding alcohols in good to excellent yields within 10 min.

Ultrasound-Assisted Solvent-Free Parallel Synthesis of 3-Arylcoumarins Using N-Acylbenzotriazoles

An ultrasound-assisted one-pot acylation/cyclization reaction between N-acylbenzotriazoles and 2-hydroxybenzaldehydes has been developed for the synthesis of substituted 3-arylcoumarins. Using ultrasound not only allows rapid and clean conversion but also simplifies experimental setup and parallel workup leading to rapid generation of 3-arylcoumarin libraries under mild, solvent-free, and chromatography-free conditions.

Bioinspired Diastereoconvergent Synthesis of the Tricyclic Core of Palodesangrens via Diels–Alder Reaction, LiAlH4-Mediated Isomerization, and Acid-Mediated Cyclization

The cyclohexene moiety of the tricyclic 6,7-diaryl-tetrahydro-6 H-benzo[ c]chromene core of palodesangrens could be assembled in a biomimetic and step-economical fashion by the Diels-Alder reaction between the electron-rich ( E)-1,3-butadienylarenes as the diene and the electron-deficient chalcones as the dienophile. During the reduction of ketone to the corresponding alcohol by LiAlH4, the mixture of endo and exo isomers underwent a novel diastereoconvergent LiAlH4-mediated isomerization to install the desired stereochemistry at C10a. Subsequent pyran ring closure under acidic conditions installed the stereochemistry at the remaining C6. Overall, the tricyclic core of palodesangrens could be prepared in three steps and up to 38% yield.

Ultrasonic-assisted synthesis of carbodiimides from N,N′ -disubstituted thioureas and ureas

A facile and efficient sonochemical method for the preparation of carbodiimides from their corresponding thioureas or ureas was described. Using Ph3P–I2 combination in the presence of triethylamine, various diaryl, aryl–alkyl, as well as dialkyl substituted substrates could be converted into carbodiimides in good-to-excellent yields within short reaction times under mild conditions with simple experimental setup.Graphical abstract