Viera Poláčková

Organocatalyst Efficiency in the Michael Additions of Aldehydes to Nitroalkenes in Water and in a Ball‐Mill

The enantioselective organocatalytic Michael addition in aqueous solution was compared with the reaction performed under solvent‐free ball‐milling conditions. A range of pyrrolidine‐derived organocatalysts were tested in the addition of aldehydes to nitroalkenes. Both procedures afforded good yields, diastereoselectivities, and enantioselectivities. The best catalyst in aqueous media was O‐lauroyl‐trans‐4‐hydroxyproline, whilst the ball‐milling technique was most‐efficient with α,α‐diphenyl‐2‐pyrrolidinemethanol trimethylsilyl ether.

Ultrasound-promoted Cannizzaro reaction under phase-transfer conditions

Abstract Ultrasound accelerates the Cannizzaro reaction of p-chlorobenzaldehyde under phase-transfer conditions. Of the three phase-transfer catalysts which were tested [benzyltriethylammonium chloride (TEBA), Aliquat and 18-crown-6] TEBA was found to be the most effective. Ferrocenecarbaldehyde and p-dimethylaminobenzaldehyde gave, under similar conditions (TEBA as the catalyst), 1,5-diaryl-1,4-pentadien-3-ones as the main product. The possible route leading to these compounds is suggested and discussed.

Microwave-Assisted Method for Synthesis of 1,3-Disubstituted Pyrroles

Abstract 1,3-Disubstituted pyrroles were prepared by a microwave-assisted reaction of pyrrolidine and aldehydes in toluene as well as in solvent-free conditions. Reactions were completed in a few minutes in the solvent-free condition but a long time (up to 30 min) was necessary to complete reactions in toluene. Yields of products depended considerably on the aldehyde used.

Pd-catalysed conjugate addition of arylboronic acids to α,β-unsaturated ketones under microwave irradiation

The Pd-catalysed conjugate addition of arylboronic acids to α,β-unsaturated cyclic ketones was studied under controlled microwave irradiation conditions. A variety of catalysts, bases and solvents was explored in order to achieve optimum yields in the shortest possible reaction time. Under optimised conditions (Pd(OAc)2/2,2′-bipyridine and KF in a mixture of toluene, water, and acetic acid and 10 min microwave irradiation), a range of arylboronic acids was successfully added to several cyclic enones. With chiral phosphane ligands, a promising enantioselectivity was obtained (85 % ee).

Effect of microwave irradiation on the reactivity of chloroarenes in Suzuki—Miyaura reaction

Simple catalytic systems for the Suzuki—Miyaura reaction of aryl chlorides under microwave conditions were tested. Microwave irradiation facilitated the reaction course. The catalyst, base, and solvent effect were studied and two reaction systems offered reasonable to high yields within a short time.

Peptide-catalyzed stereoselective Michael addition of aldehydes and ketones to heterocyclic nitroalkenes

Stereoselective Michael addition of enolizable carbonyl compounds to a furane-derived nitroalkene was catalyzed by di- and tripeptide organocatalysts. The most competent catalysts were tripeptides possessing Pro–Pro–Glu structure. With aldehydes, Michael adducts were obtained in high yields and with medium-to-high diastereo- (up to 13:1 d.r.) and enantiomeric purities (up to 99% ee). The reaction was less stereoselective with cyclic ketones than with aldehydes.Graphical abstract

Synthesis of sulfone analog of oseltamivir precursor

We describe here the synthesis of a sulfone analog of an oseltamivir precursor. The synthesis comprises cyclization of two advanced building blocks via one-pot Michael addition and Horner–Wadsworth–Emmons reaction. The first building block was synthesized by an organocatalytic Michael addition of pentyloxyacetaldehyde to a nitroalkene. The second, alkenylsulfone, building block was prepared by oxidation followed by a Mannich type reaction. The cyclization was accomplished under microwave irradiation.