Letters in Organic Chemistry - Volume 17, Issue 11, 2020

A novel series of 5-(benzo[d]thiazol-2-yl)benzo[d]oxazole-based compounds was synthesized in four linear steps in high yield from vanillin. Both benzo[d]thiazole and benzo[d]oxazole cyclizations were assisted with a domestic microwave oven in about 4-8 minutes in which the yield of the benzo[d]oxazole cyclization was up to 92%. Structures of the new synthesized compounds were elucidated by spectral data.

The micellar catalysis is well-known for its hydrophobic effect that is the tendency of nonpolar groups to cluster within the lipophilic core so as to shield them from contact with an aqueous environment formed upon the dissolution of a surfactant in water. This provides a unique opportunity to establish organic transformations in greener solvents, such as water leading to organic waste control and easy product isolation protocols. Considering the significant interaction of thiobarbituric acid moieties in a biological macromolecule core, herein, a highly efficient procedure for the synthesis of biological and medicinal important 5-(arylmethylene)dihydro-2-thioxo-4,6(1H,5H)-pyrimidinediones via Knoevenagel condensation of thiobarbituric acids and aldehydes catalyzed by a surfactant, sodium dodecyl sulfate, is developed. The synthetic procedure shows the excellent activity of the micellar catalysts towards the aldehyde activation leading to a facile condensation. The application of the method is demonstrated by further synthesis of 5,5'-(4-arylmethylene)bis[dihydro-2-thioxo-4,6(1H,5H)- pyrimidinediones]. Theoretical studies of the reaction were also carried out to investigate the effect of electron releasing and electron-withdrawing group in benzaldehyde on the reaction.

A simple and appropriate procedure for the synthesis of quinazoline-2,4(1H,3H)-dione derivatives from isocyanides, aniline and isocyanate via the Cu-catalyzed intramolecular C-H activation reaction is reported. The advantages of this method are one-pot conditions, accessible starting materials- catalyst, high yield of products, and short reaction times. The structures are confirmed spectroscopically (1H- and 13C-NMR, IR and EI-MS) and by elemental analyses.

A bifunctional squaramide catalyzed the enantioselective Michael addition of pyrazol-3- ones to ortho-quinone methides, generated in situ from 2-(1-tosylalkyl)phenols is presented. The corresponding chiral pyrazolones are obtained with good to excellent yields (27-98%) and enantiomeric excess (14-99% ee).

A method for gram scale preparation of 2-fluoropropionyl-carfentanil was established, starting from 4-phenylamino-1-benzyl-4-piperidinecarboxylic acid. 2-Fluoropropionyl-carfentanil carboxylic acid and 2-chloropropionyl-carfentanil as precursors were synthesized for the radiosynthesis of 11C and/or 18F labelled 2-fluoropropionyl-carfentanil derivatives via two separate reaction routes. Conformational analysis of 2-fluoropropionyl-carfentanil was performed using computational methods. Calculated 1H and 13C-NMR shifts are presented.

A convenient and efficient chiral CuFe2O4@SiO2-Mn(III) Ch.salen nanocatalyst has been developed for the C-N cross-coupling reactions of aryl halides/ phenylboronic acid with N-heterocyclic compounds in water and/or DMSO under mild conditions. The catalyst could be applied for the N-arylation of a variety of nitrogen-containing heterocycles with aryl chlorides, bromides, iodides and phenylboronic acid under mild conditions. Moderate to good yields were achieved for all substrates. The structure of catalyst was characterized using various techniques including FT-IR, FE-SEM, EDX, XRD, TEM and TGA. The catalyst can be simply recovered and reused for several times without significant loss of activity.

We have synthesized a library of new 1,2,3-triazole incorporated 1,3,4-thiadiazoleisothiazolo[ 4,3-b]pyridine derivatives 12a-j and have screened these products for their anticancer activities against four human cancer cell lines such as MCF-7 (breast cancer), A549 (lung cancer), DU-145 (prostate cancer), and MDA MB-231 (breast cancer) using MTT assay with etoposide as a positive control. Among them, compound 12e has shown excellent activities against MCF-7, A549, DU-145, and MDA-MB-231 with IC50 values of 0.53±0.055 μM, 0.18±0.077 μM, 0.10±0.082 μM, and 0.92±0.041 μM, respectively.

Glycosyl donors have been experimentally shown to have a high tendency for acyl transfer to the alcohol nucleophile as a major side product during glycosylation reactions. Therefore, a neighbouring group participatory mechanism of glycosylation is explored using D-galactopyranose based donor having 2-O-acyl functionality by employing density functional theory. The reaction proceeds via galactopyranosyl dioxolenium ion as a stable intermediate, which leads to the formation of α-glycoside 4, orthoester (5 or 6) and acyl transfer 7 as side products. The mechanism of the stereoselective formation of β-glycoside is investigated. Moreover, all the possible intermediates and transition states have been explored.

A catalyst system derived from commercially available Cu(NO3)2.3H2O and 2,5- dihydroxyterephthalic acid is applied to the homocoupling reaction of arylboronic acids. This transformation provides a convenient approach to symmetrical biaryls with good to excellent yields (39%- 95%), and exhibits good functional group compatibility. Furthermore, biaryl can be prepared in gram quantities in good yield.

For (Z)-(Z)-N-(λ5-phosphanylidene) formohydrazonic formic anhydride, Aza-Wittig reaction and Mumm rearrangement are studied using both density functional and coupled cluster theories. For this purpose, two different products starting from one substrate are considered that are competing with each other. The obtained products, P1 and P2, are thermodynamically favorable. The product of the aza-Wittig reaction, P1, is more stable than the product of Mumm rearrangement (P2). For the mentioned products, just one reliable pathway is separately proposed based on unimolecular reaction. Therefore, the rate constants based on RRKM theory in 300-600 K temperature range are calculated. Results show that the P1 generation pathway is a suitable path due to low energy barriers than the path P2. The first path has three steps with three transition states, TS1, TS2, and TS3. The P2 production path is a single-step reaction. In CCSD level, the computed barrier energies are 14.55, 2.196, and 10.67 kcal/mol for Aza-Wittig reaction and 42.41 kcal/mol for Mumm rearrangement in comparison with the corresponding complexes or reactants. For final products, the results of the computational study are in a good agreement with experimental predictions.

A simple and efficient methodology for Friedel-Crafts acylation of 3-methylindole using Amberlyst 15 resin as catalyst is described. This methodology shows good selectivity towards the formation of the products of 2-acylation, (3-methyl-1H-indol-2-yl)ketones. Several advantages can be ascribed to Amberlyst 15, among them; are the ease of handling, quick separation from the reaction mixture and minimum or no production of the chemical residues that must be eliminated. Besides, the catalyst can be easily recycled and reused with a minimal loss in activity through 6 reaction cycles. The catalyst was characterized by FT-IR spectroscopy and superficial acidity.