Thionation of amides using a solid-supported P2S5 reagent under microwave irradiation

In this Letter, we describe an improved method for the thionation of amides. Using a solid-supported P₂S₅ reagent, heating under microwave irradiation furnished thioamides in good to excellent yields, with a significantly reduced reaction time compared with that achieved under conventional heating. Furthermore, a change of solvent from that described in the literature enabled a simplified work-up and purification of the products.     

A microwave-assisted approach to N-(2-nitrophenyl)benzenesulfonamides that enhanced peroxidase activity in response to excess cadmium

A facile and efficient approach to N-(2-nitrophenyl) benzenesulfonamides was developed under microwave irradiation. A series of pyrabactin analogues containing nitrophenyl scaffold was obtained in excellent yields. In addition, the method was pretty suitable to prepare flusulfamide. Significantly, the 3ae could enhance POD activity in response to heavy metal stress.     

One-pot and microwave-assisted synthesis of N-sulfonylaziridines

A novel and efficient microwave-assisted one-step reaction was developed to synthesize chiral N-sulfonylaziridines by the reaction of different chiral amino alcohols and sulfonic chlorides. The newly developed microwave synthetic method has the advantage of reducing the reaction time from 24 to 0.5 h with improved yields (84-93%) and minimizing by-products.     

Ammonium salts from polymer-bound N-hydroxysuccinimide as solid-supported reagents for EDC-mediated amidations

New ammonium and alkylammonium salts derived from a polymeric N-hydroxysuccinimide (P-HOSu) have been prepared and used for the amidation of carboxylic acids and amino acids mediated by 1-ethyl-3-(3′-dimethylamino-propyl)carbodiimide hydrochloride (EDC). These polymer-supported ammonium salts afforded the corresponding amides in good yield, without detectable α-racemization and with easy recovery of the P-HOSu after the amidation reaction, being especially suitable for the amidation of Fmoc-protected amino acids.     

Use of a solid-supported coupling reagent for a selective phosphitylation of the primary alcohol of N-isobutyryl-2′-deoxy or 2′-O-methyl guanosine

We have developed a 5′-regioselective phosphitylation of 3′,5′-OH-guanosine derivatives thanks to a solid-supported coupling reagent with either a standard or a bulky phosphine. A 5′-phosphitylation up to a 95% selectivity was obtained with a quantitative conversion of starting nucleoside. After oxidation into thionophosphotriester or phosphotriester by means of solid-supported oxidizers, the 5′-phosphorylated N²-i-Bu-2′-OMe guanosines were isolated in good yields (70-80%).     

A one-pot,two-step microwave-assisted synthesis of highly functionalized benzoxazoles using solid-supported reagents (SSRs)

A one-pot, two-step protocol for the microwave-assisted solid-phase synthesis of substituted benzoxazoles has been developed starting from different polymer-bound esters we previously designed as solid-supported reagents (SSRs) for the acylation of amines, alcohols and phenols. The combination of a parallel synthesizer and a microwave reactor allowed to quickly prepare a collection of substituted benzoxaxoles in high purity and satisfactory yields. This protocol is amenable for automation and could be used for the preparation of combinatorial libraries in drug discovery programs.     

Clean and fast oxidative transformation of thiols to disulfides under solvent-free conditions

We present here a fast, solvent-free synthesis of symmetrical disulfides using solid supported catalyst (Al₂O₃/KF). The reaction was performed at room temperature, by gentle heating or under MW irradiation. This efficient and improved method is general for liquid thiols, affording the disulfides in good to excellent yields. The catalytic system can be re-used two times without previous treatment and with comparable activity.     

Exploiting microwave-assisted neat procedures: synthesis of N-aryl and N-alkylnitrones and their cycloaddition en route for isoxazolidines

Microwave irradiation allows increasing the speed of several reactions and also offers the possibility of eliminating poisoning organic solvents. In this work we report the microwave-assisted neat synthesis of α-phenyl-tert-butylnitrone (PBN) and other alkyl and aryl nitrones and also the rapid synthesis of isoxazolidines resulting from 1,3-dipolar cycloaddition of nitrones to ethyl trans-crotonate.     

TBCA mediated microwave-assisted Hofmann rearrangement

A protocol for the microwave-assisted Hofmann rearrangement mediated by TBCA/KOH/MeOH was developed. Under these conditions high yields and short reaction times were observed for aromatic benzamides.     

One-pot preparation of 2-(alkyl)arylbenzoselenazoles from the corresponding N-(acetyl)benzoyl-2-iodoanilines via a microwave-assisted methodology

We report here the first example of a one-pot synthesis of 2-(alkyl)arylbenzoselenazoles from N-(acetyl)benzoyl-2-iodoanilines. The reaction was carried out in the presence of Woollins’ reagent under microwave irradiation and resulted in moderate to good yields.     

Pd/Nb2O5: efficient supported palladium heterogeneous catalyst in the production of key intermediates for the synthesis of ‘sartans’ via the Suzuki reaction

Pd/Nb₂O₅ was prepared, characterized and tested in Suzuki-Miyaura cross-coupling reactions under ligand-free conditions. High yields and selectivities were observed within short reaction times and very low palladium loadings.     

Cold microwave chemistry: synthesis using pre-cooled reagents

A novel experimental procedure for chemical reactions has been devised that involves mixing and then freezing the reagents (organic solvent-free) to a sub-zero temperature such as −30 °C. This frozen mixture is exposed to microwave irradiation for a brief period of time. The use of pre-cooled reagents may give a single product not obtained by traditional microwave irradiation at room temperature. Interestingly, such a product may provide information about mechanisms by identifying the first step of a multiple step reaction.     

A very simple and highly efficient procedure for N-formylation of primary and secondary amines at room temperature under solvent-free conditions

N-Formylation of primary and secondary amines has efficiently been carried out at room temperature in excellent yields by using catalytic amount of sodium formate in formic acid under solvent-free conditions. The process is remarkably simple and environmentally benign.     

Synthesis and olefination of carbonyl compounds using solid-supported reagents

The development and application of three new solid-supported reagents for use in the synthesis or olefination of carbonyl compounds are described. The reagents include the Weinreb amide, Mukaiyama's S-2-pyridyl thioate and a Peterson methylenation reagent. As solid-supports p-benzyl alcohol resin, Wang resin and Merrifield resin (1-2% crosslinked polystyrene) have been used.     

Base-promoted N-alkylation using formamides as the N-sources in neat water

An efficient catalyst-free, alternative method for the C–N bond formation reaction of alkyl electrophiles using formamides as the N-sources was achieved under mild conditions. The reaction possesses the advantages of a broad range of substrates scope and wide functional group tolerance. It should also be noted that this process was performed using the environmentally benign water as the sole solvent, and high yield can also be achieved in ten-gram scale.     

Microwave assisted Suzuki reaction in N-butylpyridinium salts/water systems

A solvent mixture containing the ionic liquid derived from 4-picoline (C₄MPyBF₄) and water was tested for the Suzuki-Miyaura reaction under microwave irradiation. This solvent system led to very high conversions and clean reactions. When compared with the other more common ionic liquid, such as C₄MImBF₄, C₄MPyBF₄ proved to be superior.     

Water promoted, microwave-assisted oxidative novel deamination of N-aminoquinazolinones

A novel deamination of 2-alkyl/aryl 3-amino-4（3H）-quinazolinones series using aqueous KMnO4 under thermal condition and microwave irradiation is described. Compared to thermal condition, significantly higher yields in much shorter times were observed for reactions under microwave irradiation. A plausible mechanism has been proposed for the oxidative water-promoted deamination.     

One-pot synthesis of N-allylthioureas using supported reagents

A simple and efficient method has been developed for the synthesis of N-allylthioureas from allylic bromides in one-pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which allyl bromide reacts first with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give the final product, N-allylthiourea, in good yield.     

A rapid and simple amine-catalyzed microwave-assisted isomerization of maleamides into fumaramides

An improved, efficient, and simple method for the synthesis of nonsymmetrical diamides of fumaric acid is reported. Starting from commercially available substrates, maleic diamides are formed in two steps, and then isomerized in a focused microwave reactor in acetonitrile as the solvent in the presence of a catalytic amount of piperidine, giving the corresponding fumaramides in high yields and purity.