Solvent-free microwave-mediated Michael addition reactions

Beneficial Contribution of Biosourced Ionic Liquids and Microwaves in the Michael Reaction

We developed a synthesis of chiral ionic liquids from proline and one of its derivatives. Nine chiral ionic liquids were synthesized with yields from 78% to 95%. These synthesized ionic liquids played two roles in Michael reactions, as solvents, and as basic catalysts, where the ionic phase could also be reused at least five times without loss of activity. The yields up to 99% were improved by increasing the amount of dimethylmalonate from 1.2 equivalents to 3 or 4 equivalents. Furthermore, the reaction time could be reduced from 24 h to 45 min through microwaves activation.

Modification of bio-based β-diketone from wheat straw wax: synthesis of polydentate lipophilic super-chelators for enhanced metal recovery

Bio-derived lipophilic polydentate chelators have been synthesized and tested for their chelating ability using a range of metal salts of Cu, Co, Ni, Fe, and Cr. These novel molecules were produced by the Michael addition reaction of 14,16-hentriacontanedione, isolated from wheat straw wax, with methyl acrylate or bio-derived dimethyl itaconate via microwave heating. The Michael adducts could either be used directly as esters or be hydrolysed to their acid form. Critically, the creation of additional binding sites via the carboxylate moieties leads to an enhanced metal uptake over both a non-renewable commercially available lipophilic β-diketone (dibenzoylmethane) and the unmodified hentriacontane-14,16-dione, for the chelation of Fe(iii), Cr(iii) and Ni(ii). The modified β-diketone containing a single carboxylic acid functionality was able to extract 167 mg L-1 of Fe(iii) from an FeCl3 solution with no pH adjustment. In comparison, no chelation was observed with dibenzoylmethane, while unmodified hentriacontane-14,16-dione was able to extract 81 mg L-1. The modified chelators containing one and two ester carboxylates extracted 255 and 305 mg L-1 Cr(iii) from a solution of CrCl3 at pH 5-6, 238 mg L-1 was extracted by the unmodified β-diketone whilst no extraction was observed using dibenzoylmethane. This suggest some minor contribution or positive effect to chelation due to neighbouring ester groups. The chelator containing two carboxylic acid groups (tetra-dentate when combined with the diketone) was the most proficient in this study for removal of Ni from an NiCl2 solution (140 mg L-1). It was also found that at higher pH almost quantitative extraction was achieved using the polydentate chelators.

In situ formed acetals facilitated direct Michael addition of unactivated ketones

A facile Michael addition of unactivated ketones under Brønsted acid conditions for the synthesis of 1,5-diketones.

On the Effect of Microwave Energy on Lipase-Catalyzed Polycondensation Reactions

Microwave energy (MWe) is, nowadays, widely used as a clean synthesis tool to improve several chemical reactions, such as drug molecule synthesis, carbohydrate conversion and biomass pyrolysis. On the other hand, its exploitation in enzymatic reactions has only been fleetingly investigated and, hence, further study of MWe is required to reach a precise understanding of its potential in this field. Starting from the authors’ experience in clean synthesis and biocatalyzed reactions, this study sheds light on the possibility of using MWe for enhancing enzyme-catalyzed polycondensation reactions and pre-polymer formation. Several systems and set ups were investigated involving bulk and organic media (solution phase) reactions, different enzymatic preparations and various starting bio-based monomers. Results show that MWe enables the biocatalyzed synthesis of polyesters and pre-polymers in a similar way to that reported using conventional heating with an oil bath, but in a few cases, notably bulk phase polycondensations under intense microwave irradiation, MWe leads to a rapid enzyme deactivation.

Antimycobacterial evaluation of novel [4,5-dihydro-1H-pyrazole-1-carbonyl]pyridine derivatives synthesized by microwave-mediated Michael addition

The focus of this study is the synthesis and biological activity evaluation of a series of dibenzalaceton derivatives (3a-3n) and novel [4,5-dihydro-1H-pyrazole-1-carbonyl]pyridine derivatives (5a-5g) against Mycobacterium bovis, Bacillus Calmette-Guerin (BCG). Dibenzalacetone derivatives were synthesized by benzaldehyde derivatives. The [4,5-dihydro-1H-pyrazole-1-carbonyl]pyridine derivatives were synthesized by Michael addition reaction and using green chemistry microwave-mediated method. All compounds were evaluated against BCG and the activity expressed as minimum inhibitory concentration (MIC) in μM. The result showed good activity for all the compounds especially compounds (3a), (3n), and (5a) illustrated high activity (7.03, 8.10 and 5.37 μM, respectively).

TiO2 nano crystallites catalyzed water mediated microwave assisted regioselective three component domino hydrolysis/aldol condensation/Michael addition reaction of 3-(1,5-dioxo-1,5-diphenylpentan-3-yl)quinolin-2(1H)-one

Microwave supported, water intervened, nano crystalline TiO₂ catalyzed synthesis of 3-(1,5-dioxo-1,5-diphenylpentan-3-yl)quinolin-2(1H)-ones, is described.

Unimolecular dissociation of protonated trans-1,4-diphenyl-2-butene-1,4-dione in the gas phase: rearrangement versus simple cleavage

Fragmentation mechanisms of trans-1,4-diphenyl-2-butene-1,4-dione were studied using a variety of mass spectrometric techniques. The major fragmentation pathways occur by various rearrangements by loss of H(2)O, CO, H(2)O and CO, and CO(2). The other fragmentation pathways via simple alpha cleavages were also observed but accounted for the minor dissociation channels in both a two-dimensional (2-D) linear ion trap and a quadrupole time-of-flight (Q-TOF) mass spectrometer. The elimination of CO(2) (rather than CH(3)CHO or C(3)H(8)), which was confirmed by an exact mass measurement using the Q-TOF instrument, represented a major fragmentation pathway in the 2-D linear ion trap mass spectrometer. However, the elimination of H(2)O and CO becomes more competitive in the beam-type Q-TOF instrument. The loss of CO is observed in both the MS(2) experiment of m/z 237 and the MS(3) experiment of m/z 219 but via the different transition states. The data suggest that the olefinic double bond in protonated trans-1,4-diphenyl-2-butene-1,4-dione plays a key role in stabilizing the rearrangement transition states and increasing the bond dissociation (cleavage) energy to give favorable rearrangement fragmentation pathways.