Grzegorz Mlostoń

New thione chemistry

Rate measurements reveal the superiority of C = S bonds over CC multiple bonds as dipolarophiles in cycloadditions of thiobenzophenone S-me- thylide, diphenyldiazomethane, and N-methyl-C-phenylnitrone. Thione S-oxi- des (sulfines) and thione S-sulfides likewise prefer thiones as cycloaddition partners. Many cycloadditions of thiones .approach equilibria; the high reacti- vity is a kinetic phenomenon, the low HO-LU distance of the a-MOs being re- sponsible. Ab initio calculations for %C=S + %C=NH+-O- result in a ne- gative activation energy. a Bonds with silicon, phosphorus etc. exhibit likewise low HO-LU gaps and increased reactivity.

Synthesis and evaluation of antimicrobial activity of hydrazones derived from 3-oxido-1H-imidazole-4-carbohydrazides

In this work we reported the synthesis and evaluation of in vitro antimicrobial activities of hydrazones 6 obtained from 3-oxido-1H-imidazole-4-carbohydrazides 4. All new compounds were characterized by spectroscopic methods. Hydrazones 6 were tested for their in vitro antimicrobial activity against four Gram-positive and four Gram-negative strains of bacteria as well as one fungal species. Three of the tested compounds appeared to be promising agents against reference strains of Escherichia coli, Staphylococcus aureus and Staphylococcus epidermidis. They were also tested against twelve clinical isolates of S. aureus and their cytotoxic effect on murine fibroblasts and HeLa human tumor cell line was determined.

Cycloadditions of two thiocarbonyl ylides with α,β-unsaturated esters and nitriles: steric course and mechanism ☆

Abstract In the probably concerted cycloadditions of the sterically hindered thiocarbonyl ylide 1 with fumaronitrile, maleonitrile, and dimethyl fumarate, the dipolarophile configuration is retained whereas retention/inversion 99:1 for dimethyl maleate (51 times less reactive than fumarate) signals a small involvement of a two-step pathway. The latter becomes dominant when two acceptor groups stabilize the anionic terminus of a zwitterionic intermediate. Nonstereospecific cycloadditions of 1 with dimethyl 2,3-dicyanofumarate ( 16 , retention/inversion 60:40) and dimethyl 2,3-dicyanomaleate ( 17 , 76:24) were observed. Special conditions were required to avoid a preceding cis, trans isomerization, 16 ⇄ 17 , catalyzed by thiadiazoline 4 , the precursor of 1 . In the case of the related thiocarbonyl ylide 37 , this catalysis could not be suppressed and the same ratio of adducts (55:45) was obtained with 16 and 17 .

Thioformaldehyde S‐sulfide (Thiosulfine)

Matrix isolation spectroscopy allows the direct identification of ylide 1 and its cyclic isomer 2. They were obtained by pyrolysis of 1,2,4-trithiolane under high vacuum; the cyclic compound forms from 1 by thermal ring closure in a kinetically controlled reaction.

Synthesis of Imidazole Derivatives Using 2‐Unsubstituted 1H‐Imidazole 3‐Oxides

The reaction of 1,4,5-trisubstituted 1H-imidazole 3-oxides 1 with Ac2O in CH2Cl2 at 0 - 5° leads to the corresponding 1,3-dihydro-2H-imidazol-2-ones 4 in good yields. In refluxing Ac2O, the N-oxides 1 are transformed to N-acetylated 1,3-dihydro-2H-imidazol-2-ones 5. The proposed mechanisms for these reactions are analogous to those for N-oxides of 6-membered heterocycles (Scheme 2). A smooth synthesis of 1H-imidazole-2-carbonitriles 2 starting with 1 is achieved by treatment with trimethylsilanecarbonitrile (Me3SiCN) in CH2Cl2 at 0 - 5° (Scheme 3).

The Formation of 1,3‐Dithiolanes from Aromatic Thioketones and Diazomethane − The Mechanism of the Schönberg Reaction

Reactions of diaryl thioketones with diazomethane at room temperature afford 4,4,5,5-tetraaryl-1,3-dithiolanes; the scope of this surprising 2:1 interaction has been studied for decades (Schonberg Reaction). The clue to the mechanism was our observation that the stoichiometry is 1:1 at −78 °C, and 2,5-dihydro-2,2-diaryl-1,3,4-thiadiazoles are formed as primary [2+3] cycloadducts. They lose N2 at −45 °C in first-order reactions generating diaryl thioketone S-methylides which can be intercepted by thioketones (1,3-dithiolanes), multiple CC bonds, or acids HX. In the absence of trapping reagents, the elusive intermediates either dimerize furnishing 2,2,3,3-tetraaryl-1,4-dithianes or give rise to 2,2-diarylthiiranes by electrocyclization. Beyond thiobenzophenone and diazomethane, our main model reaction, the studies involve fluorene-9-thione, 4,4-dimethoxy- and 4,4-dichlorothiobenzophenone. The ring of 2,5-dihydro-2,2-diphenyl-1,3,4-thiadiazole (8) is opened by LDA at −78 °C and derivatives of anion 12 are obtained. − In summa: The Schonberg reaction consists of two 1,3-dipolar cycloadditions, linked by a 1,3-dipolar cycloreversion.

Open-chain aliphatic thiones and diazomethane; reactions of 1,3,4-thiadiazolines and thiocarbonyl ylides

Abstract Diazomethane adds in two directions to R 2 C=S, R = ethyl, propyl, isopropyl, tert -butyl; the dependence of the regioisomer ratio on R and on solvent polarity discloses the nature of the orienting forces. The thione- S -methylides generated by N 2 extrusion from 1,3,4-thiadiazolines undergo 1,4-H shift or electrocyclization.

Selected cyclic oligosulfides and oligosulfide S-oxides and their reactions with (Ph3P)2Pt(η2-C2H4)

Abstract Syntheses of cyclic organic oligosulfides like dithiiranes, 1,2,4-trithiolanes, 1,2,4,5-tetrathianes, 1,2,3,5,6-pentathiepanes and their mono S-oxides are described. Their reactivity toward the platinum(0) compound (Ph 3 P) 2 Pt(η 2 -C 2 H 4 ) has been investigated. Insertion of the platinum(0) moiety into the sulfur–sulfur bond leads to dithiolato, sulfenato-thiolato as well as thiocarbonyl and sulfine platinum complexes. The reaction patterns of the sulfur containing heterocycles with the above metal complex are discussed.

Reactions of 2-Unsubstituted 1 H -Imidazole 3-Oxides with Heterocumulenes and Dimethyl Acetylenedicarboxylate

Reaction of 2-unsubstituted 1H-imidazole 3-oxides with isocyanates, isothiocyanates, and dimethyl acetylenedicarboxylate led to the formation of 2-functionalized imidazole derivatives. Stepwise reaction mechanisms via zwitterionic intermediates are proposed. The intermediate [3+2] cycloadducts stabilize via extrusion of COX or ring opening.

1,3-cycloadditions of aliphatic thione S-methylides to dimethyl 2,3-dicyanofumarate and 2,3-dicyanomaleate; a test case for steric course and mechanism☆

Abstract The 1,3-cycloadditions of thione S-methylides 2 and 9 to dimethyl 2,3-dicyanofumarate and 2,3-dicyanomaleate are nonstereospecific. A preceding cis,trans isomerization of the unsaturated dipolarophiles catalyzed by the thiadiazolines (precursors of the thione S-methylides) had to be suppressed in order to clarify the stereochemical leakage during the cycloaddition.