Synthesis and Reactivity of 3H-1,2-Dithiole-3-Thiones

3H-1,2-Dithiole-3-thiones are among the best studied classes of polysulfur-containing heterocycles due to the almost explosive recent interest in these compounds as sources of hydrogen sulfide as an endogenously produced gaseous signaling molecule. This review covers the recent developments in the synthesis of these heterocycles, including both well-known procedures and important novel transformations for building the 1,2-dithiole-3-thione ring. Diverse ring transformations of 3H-1,2-dithiole-3-thiones into various heterocyclic systems through 1,3-dipolar cycloaddition, replacement of one or two sulfur atoms to form carbon- and carbon-nitrogen containing moieties, and other unexpected reactions are considered.

The First Step of Biodegradation of 7-Hydroxycoumarin in Pseudomonas mandelii 7HK4 Depends on an Alcohol Dehydrogenase-Type Enzyme

Coumarins are well known secondary metabolites widely found in various plants. However, the degradation of these compounds in the environment has not been studied in detail, and, especially, the initial stages of the catabolic pathways of coumarins are not fully understood. A soil isolate Pseudomonas mandelii 7HK4 is able to degrade 7-hydroxycoumarin (umbelliferone) via the formation of 3-(2,4-dihydroxyphenyl)propionic acid, but the enzymes catalyzing the α-pyrone ring transformations have not been characterized. To elucidate an upper pathway of the catabolism of 7-hydroxycoumarin, 7-hydroxycoumarin-inducible genes hcdD, hcdE, hcdF, and hcdG were identified by RT-qPCR analysis. The DNA fragment encoding a putative alcohol dehydrogenase HcdE was cloned, and the recombinant protein catalyzed the NADPH-dependent reduction of 7-hydroxycoumarin both in vivo and in vitro. The reaction product was isolated and characterized as a 7-hydroxy-3,4-dihydrocoumarin based on HPLC-MS and NMR analyses. In addition, the HcdE was active towards 6,7-dihydroxycoumarin, 6-hydroxycoumarin, 6-methylcoumarin and coumarin. Thus, in contrast to the well-known fact that the ene-reductases usually participate in the reduction of the double bond, an alcohol dehydrogenase catalyzing such reaction has been identified, and, for P. mandelii 7HK4, 7-hydroxycoumarin degradation via a 7-hydroxy-3,4-dihydrocoumarin pathway has been proposed.

Synthesis of Nitroaromatic Compounds via Three-Component Ring Transformations

1-Methyl-3,5-dinitro-2-pyridone serves as an excellent substrate for nucleophilic-type ring transformation because of the electron deficiency and presence of a good leaving group. In this review, we focus on the three-component ring transformation (TCRT) of dinitropyridone involving a ketone and a nitrogen source. When dinitropyridone is allowed to react with a ketone in the presence of ammonia, TCRT proceeds to afford nitropyridines that are not easily produced by alternative procedures. Ammonium acetate can be used as a nitrogen source instead of ammonia to undergo the TCRT, leading to nitroanilines in addition to nitropyridines. In these reactions, dinitropyridone serves as a safe synthetic equivalent of unstable nitromalonaldehyde.

REACTION OF 2-HETARYL-2-(DIHYDROFURAN-2(3H)-ILIDEN)ACETONITRILES WITH AROMATIC AMINES

This article reports on the reaction of 2-hetaryl-2-(furanyl-2-ylidene)acetonitriles with aromatic amines as N-nucleophiles. 2-Hetaryl-2-(furanyl-2-ylidene)acetonitriles represent versatile building blocks in syntheses of ω-(N-aryl)alkyl substituted heterocycles due to the presence of 1,3-bielectrophilic acrylonitrile fragment functionalized with unsaturated heterocyclic ring and nucleophilic azaheterocyclic moiety. The carbonyl group masked within the N-arylpyrrolidinylidene fragment which undergoes a ring opening through the reaction with nucleophiles. So, a method for the synthesis of 2-hetaryl-6-hydroxy-3-(arylamino)hex-2-enenitriles and 2-hetaryl-2-(N-arylpyrrolidin-2-ylidene)acetonitriles has been developed by us. The proposed scheme is based on the available reagents using. As a result of Michael addition, the aromatic amines to 2-hetaryl-2-(furanyl-2-ylidene)acetonitriles followed by ring transformations has formed two types of products, depending on the reaction conditions. The reaction of substituted furanylylideneacetonitriles with aromatic amines proceeds in good to high yields affording the corresponding 3-(arylamino)hex-2-enenitriles and 2-(N-arylpyrrolidin-2-ylidene)acetonitriles derivatives. The stereochemistry of the ring-opening reaction follows the rules of a classical SN2 mechanism. The resulting linear products can be cyclized to 2-hetaryl-2-(furanyl-2-ylidene)acetonitriles in high yields by treatment with the catalytic amount of acid or the equimolar amount of aromatic amines. Under these conditions 2-hetaryl-6-hydroxy-3-(arylamino)hex-2-enenitriles arising from reaction gives the ring closure. Since both ring-opening and cyclisation occur with fixed stereochemistry the reaction appears a valuable modification to the preparation of acetonitriles derivatives.

Synthesis of Alkoxycarbonyldifluoromethyl-Substituted Semisquarates and Their Transformations

A novel EtO2CCF2-substituted semisquarate is synthesized from diisopropyl squarate by selective 1,2-addition of the Reformatsky reagent derived from BrCF2CO2Et and subsequent rhenium-catalyzed allylic alcohol rearrangement. The compatibility of the highly reactive EtO2CCF2 group in ring transformations of the obtained semisquarate is investigated. Various EtO2CCF2-substituted, highly functionalized compounds, such as quinones, tetronates, cyclopentenones and a bicyclo-[3.2.0]heptenone, are successfully synthesized by ring transformations of the EtO2CCF2-substituted semisquarate. Also, an allylO2CCF2-substituted semisquarate is prepared and converted into the corresponding tetronate. Subsequent palladium-catalyzed deallylation followed by condensation of the resulting carboxylic acid with several amines under mild conditions affords the corresponding α,α-difluoroamides in good yields.

Pyrrolidine and oxazolidine ring transformations in proline and serine derivatives of α-hydroxyphosphonates induced by deoxyfluorinating reagents

Diastereoselective reactions of hydroxyphosphonates from proline or serine with fluorinating agents yielding piperidine-, oxazolidine-, aziridine- or sulfonate phosphonates were reported.