THE SOLVOLYSIS AND NUCLEOPHILIC SUBSTITUTION IN SERIES OF CYCLIC HALOGENALKYLISOTHIOUREAS

Abstract

Previously we reported 1, that solvolytic rearrangement of salts and bases of 2-amino-5-X-5,6-dihydro-4-H-1,3-thiazines \I a,b, where a X=C1, b X=Br\ proceeds with a contraction of cycle and results in salts and bases of 2-amino-5-X-methyl-2-thiazolines \II a-c, where a X=C1, b X=Br, c X=OH\. The reversibility of this reaction is shown now. It was found by means of radiochromatography that hydrolysis of ³⁵S-labelled IIb bromide gives rise to rearranged Ib besides hydrolytic product lie. It was shown, also, that the solvolysis of salts IIa,b in 50% aqueous ethanol, when excess of Na³⁶Cl is present, gives both ordinary substitution products and certain amount of rearranged Ia. In the course of ³⁵-labelled IIb bromide solvolysis in the same conditions the return of bromide ions takes place. It was found that the addition of salts affects the composition of Ib bromide hydrolysis products. This testifies that the composition of reaction products depends on the episulphonium III form present in the medium \ scheme\. It is possible, that the formation of covalent system I is most probably due to internal return from IIIa, but covalent form II results from the other steps of the dissociation. This is confirmed by absence 2-amino-5-hydroxy-5,6-dihydro-4-H-1,3-thiazine in reaction mixture. The addition of NaC10₄ and NaNO₃ supresses bromine ions return owing to ion exchange resulting in new external pair IIId, what leads to the increase of the relative amount of IIc. On the other hand the addition of KBr and NaCl decrease the amount of IIc, due to the increase of the degree of ions return and the probability of halogen ions attack to episulphonium III.     

ZrOCl2·8H2O in water: An efficient catalyst for rapid one-pot synthesis of pyridopyrazines,pyrazines and 2,3-disubstituted quinoxalines

Zirconium(IV) oxide chloride was found to be a rapid and efficient catalyst for the synthesis of pyrazines and 2,3-disubstituted quinoxalines in water. A variety of pyridopyrazine and 2,3-disubstituted quinoxaline derivatives are readily prepared in high yields under green conditions by cyclocondensation of the desired 1,2-diamine and 1,2-diketone using a catalytic amount of zirconium(IV) oxide chloride in water. Less active diamines, such as 2,3- and 3,4-diaminopyridines took part in this protocol to provide the desired products in good to excellent yields.     

Catalytic cyanosilylation of ketones with simple phosphonium salt

In the presence of 1-5 mol % of benzyltriphenylphosphonium chloride, a wide variety of unconjugated and conjugated, acyclic and cyclic ketones were transformed to their corresponding cyanohydrin silyl ethers in excellent yields.     

Cyclobutanone, cyclobutylidene and oxo species on β-Mo2C

The adsorption and dissociation of cyclobutanone on a β-Mo₂C foil was studied using RAIRS, XPS and TPD. Adsorption at 105 K populates η¹ and η² states in a 5:1 ratio. Heating to 170-300 K causes scission of the carbonyl bond and the development of RAIRS spectra characteristic of a cyclobutylidene-oxo surface complex. This dissociation chemistry is compared to literature data for the interaction of ketones with a single-metal atom tungsten complex.     

Synthesis of C2-symmetric 1,4-diketones from tartaric acid dichloride

Cross-coupling reactions of tartaric acid dichloride with organocopper reagents, derived from Grignard reagents, cuprous bromide and lithium bromide, provide a simple and straightforward method for the synthesis of C₂-symmetric 1,4-diketones.     

Synthesis of 2-amino-5-alkylidenethiazol-4-ones from ketones, rhodanine, and amines with the aid of re-usable heterogeneous silica-pyridine based catalyst

A new methodology has been developed towards the synthesis of novel 2-amino-5-alkylidenethiazol-4-ones from ketones, amines, and rhodanine. This is the first report of the use of ketones in contrast to aldehydes in all the earlier reported procedures. A new heterogeneous dipolar catalyst is designed and synthesized for this reaction. The unique properties of this catalyst facilitate the synthesis of such compounds. These 5-alkylidene rhodanine precursors display wide range of biological activities to possess antiviral, antimicrobial, cardiotonic and anti-inflammatory effects.     

Synthesis and characterization of permethylated 1,3,5-tri- and 1,3,5,7-tetracarbonyl compounds

Permethylated 1,3,5-tri- and 1,3,5,7-tetracarbonyl compounds were prepared and structurally characterized. 2,2,4,4-Tetramethyl-3,5-dioxoesters were prepared by condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with acid chlorides and subsequent reaction with methyl iodide. 2,2,4,4,6,6-Hexa-substituted 3,5-dioxopimelates were prepared by condensation of 1,3-bis(trimethylsilyloxy)-1,3-butadienes with methyl 3-chloro-3-oxopropanoate and subsequent methylation. The use of caesium carbonate as the base for the methylation proved to be important to achieve good yields. The conformation of the products was studied by experimental and theoretical methods (DFT calculations).     

Sulfamic acid:An efficient,cost-effective and green catalyst for crossed-aldol condensation of ketones with aromatic aldehydes under solvent-free

Aromatic aldehydes undergo crossed-aldol condensation with ketones in the presence of catalytic amount of sulfamic acid(SA) to afford the correspondingα,β-unsaturated aldol products under solvent-free conditions in good to high yields at 45-80℃.     

1,2-Dibromoethane and KI mediated α-acyloxylation of ketones with carboxylic acids

The 1,2-dibromoethane-and Kl-mediatedα-acyloxylation of ketones is reported in moderate to good yield without the use of transition metals and strong oxidants.Various acids are well tolerated with wide functional group compatibility.An 1,2-dibromoethane-and Kl-catalysed reaction mechanism is proposed based on the results of control experiments.     

Interaction of push–pull <Emphasis Type="Italic">tert-</Emphasis>enamines with phenylglyoxal

Abstract  The reaction of push–pull enamines with 1,2-biselectrophilic phenylglyoxal was investigated. Phenylglyoxal was found to react depending on the structure of the push–pull enamine, affording either a hydroxyalkylation product at the methyl group or the cyclic product via participation of the methyl group and the β-carbon of the enamine. Graphical abstract