Marek Stankevič

Reduction of functionalized tertiary phosphine oxides with BH3.

A direct stereoselective conversion of tertiary hydroxyalkylphosphine oxides to the corresponding tertiary hydroxyalkylphosphine-boranes involving facile reduction of the P═O bond by BH3 under mild conditions has been developed. The unprecedented facility of reduction of the strong P═O bond by BH3, a mild reducing agent, has been achieved through an intramolecular P═O···B complexation directed by proximal α- or β-hydroxy groups present in the phosphine oxide structures. As established by two chemical correlations, the developed transformation of hydroxyalkylphosphine oxides into hydroxyalkylphosphine-boranes takes place with complete inversion of configuration at P.

Michael-type addition of secondary phosphine oxides to (1,4-cyclohexadien-3-yl)phosphine oxides.

Base-induced reaction between (1,4-cyclohexadien-3-yl)phosphine oxides and secondary phosphine oxides gives 3,4-bis(phosphinoyl)cyclohexenes and 2,3-bis(phosphinoyl)cyclohexenes through an in situ isomerization of one of the cyclohexadienyl double bonds and a subsequent Michael-type addition of the secondary phosphine oxide.

Stereoselectivity of Michael Addition of P(X)–H-Type Nucleophiles to Cyclohexen-1-ylphosphine Oxide: The Case of Base-Selective Transformation

Michael addition of phosphorus nucleophiles to the unsymmetrically substituted tert-butyl(1,4-cyclohexadien-3-yl)phosphine oxide and its derivatives has been described. The addition proceeds with the formation of the mixture of two isomeric products with good yield and diastereoselectivity. The reaction of tert-butyl(cyclohexen-1-yl)methylphosphine oxide with phosphorus nucleophiles is base sensitive and might afford two epimers which differ at one chirality center. The absolute configuration of the products has been assigned on the basis of conformational and (1)H NMR analysis, and the mechanism of the reaction has been discussed. The Michael addition of phosphorus nucleophiles is postulated to proceed with or without consecutive epimerization of two α-carbanions.

Formation of aqueous and alcoholic adducts of curcumin during its extraction

Curcumin is a phenolic compound produced by some plants, among which Curcuma longa is the reachest in this principal curcuminoid. Curcumin is known from its lability, however, the structural curcumin transformations and the formation of hydroxy and alkoxy adducts has not been reported yet. The formation of the mentioned derivatives is favoured by an alkaline environment. The presented results are important both from the analytical and food processing point of view as curcumin transformation products can be mistakenly treated as new components naturally present in turmeric, while in fact they may be formed during food products preparation, causing consumer misinformation about their bioactivity. In this context, an attempt has been made to investigate this problem. The present paper shows that curcumin easily transforms into ketonic/enolic structural isomers and forms adducts with water and alcohols. All structures of these compounds were confirmed by MSn, HRMS and partly also by NMR data.

P-Arylation of secondary phosphine oxides catalyzed by nickel-supported nanoparticles

A protocol for the cross coupling of aryl halides with secondary phosphine oxides over Ni/CeO2 or Ni/Al2O3 catalysts has been developed for the first time. The advantages offered using this protocol are operational simplicity and the use of an inexpensive heterogeneous nickel catalyst in the absence of any additional ligand. A range of aryl bromides and iodides are coupled with secondary phosphine oxides using low loadings of a catalyst (1 mol%) via this procedure, with good to high yield (up to 86%). Moreover, the influence of nickel particle size and catalyst support on P-arylation of secondary phosphine oxides has also been established.

Possibility of quinine transformation in food products: LC–MS and NMR techniques in analysis of quinine derivatives

Quinine is an alkaloid consisting of two major systems: quinoline and quinuclidine. It receives the attention of scientists because of its several medical properties: antimalarial, painkilling and fever-reducing properties. Moreover, it is widely used in food industry as a flavor component. Although the method of quinine synthesis is known, the most cost-effective is its isolation from its natural source, the bark of Cinchona tree. Liquid–solid extraction is the predominantly applied method for the isolation of active biological compounds from different plants. We found that the heating of the quinine in phosphoric buffer solution with low pH produced at least five compounds, whereas the heating of the quinine in alcohol/phosphoric buffer solution with decreased pH produced at least eight compounds. The formation of hydroxy and alkoxy adducts has not yet been reported. We observed that the amount of each formed component is dependent on the heating time, alcohol concentration in alcoholic/buffer mixture and pH. The presented results are particularly important in the context of the use of quinine as food ingredient, because quinine derivatives, quinine structural isomers and their derivatives can be formed in significant amounts and their influence on the human body has not been fully explored yet.

Intramolecular Nucleophilic Substitution of ω-Haloalkylphosphine Derivatives

ω-Haloalkylphosphine derivatives undergo the intramolecular nucleophilic substitution reaction upon treatment with a strong base, yielding either cycloalkylphosphine derivatives or heterocyclic phosphine derivatives. The selectivity of the cyclization of (ω-haloalkyl)alkylarylphosphine derivatives depends strongly on the distance between the electrophilic and nucleophilic carbon atoms and the structure of the phosphorus moiety. The desymmetrization of dimethylphenylphosphine sulfide followed by haloalkylation and cyclization led to the enantiomerically enriched tertiary phosphine sulfide, possessing a cyclohexyl fragment at the phosphorus.